The Fires of Pompeii (TV story)

The Fires of Pompeii was the second episode of series 4 of Doctor Who.

Narratively, the story was important for explaining why the Doctor can sometimes change history and at other times cannot. Specifically, it introduced the notion of "fixed points" in time, which would later be the central theme of the television stories The Waters of Mars and The Wedding of River Song. It also continued the "Missing Planets" arc, with the Pyroviles mentioning their home planet having been taken much like the Adipose's breeding planet.

The episode also introduced the idea of "the destiny trap"; the Doctor and Donna arrived in Pompeii fully aware of what was to happen. Because of this, they were unable to change events once they'd become part of them, although they were able to save at least one person and their family. This concept would later be mentioned by the Eleventh Doctor in The Time of the Doctor regarding the Silence and how their efforts to kill him had created the event they tried to erase.

Behind the scenes, the episode was notable for being the first major shoot outside the United Kingdom since the 1996 telemovie. Moreover, it was the first time a principal photography unit had been outside its country of production since The Two Doctors.

The episode notably featured the first appearance of two actors within the series that went on to play bigger roles during the show's later seasons. It hosted a guest appearance from Karen Gillan, who would later star as the Eleventh Doctor's companion, Amy Pond, in series 5, 6 and 7. It also featured a guest appearance of Peter Capaldi, who would later portray the twelfth incarnation of the Doctor, and the fact he shared the appearance of a character in this story was not ignored. This would become an important aspect of that Doctor's identity when he made the connection that his face was taken from someone he previously met.

Synopsis
The Tenth Doctor tries taking Donna Noble to ancient Rome for her first trip in the TARDIS, but seems to have miscalculated. Instead of seven hills, they find a single mountain billowing smoke — Vesuvius. They're in Pompeii, 23 August 79 AD: the day before "Volcano Day". However, something else is horribly wrong. The Soothsayers' predictions seem to always be correct... so why can't they see tomorrow's disastrous events, the eruption of Vesuvius, the death of their city? What is blocking their perception, and will the TARDIS team be able to walk away from a fixed point in time, saving no one from certain doom? Well, Donna has something to say about that!

Plot
The Tenth Doctor and Donna exit the TARDIS in what the Doctor claims is 1st century Rome. Donna is amazed to have gone back in time; everyone around them is long dead, from her perspective of being from the 21st century. Joking not to tell the locals that, the Doctor watches as Donna takes in the sights. When Donna expresses scepticism due to English words she notices on a cart, the Doctor explains that the TARDIS translation circuits are translating the local language for her; they're actually currently speaking Latin. This amazes Donna further.

A new idea forms in her head — what if she said something in actual Latin while her speech is being translated? The Doctor honestly hasn't a clue, noting she likes to ask the hard questions. Smirking that she actually managed to stump the Doctor, Donna decides to try it out by saying "Veni, vidi, vici" to a nearby stallholder, who tells her, emphasising each syllable, that he doesn't speak Celtic. The Doctor explains that she sounded Welsh — "there's something".

Resuming their walk, Donna wonders if they stand out because of their clothing, but the Doctor explains that Rome is "like Soho, but bigger". The Doctor explains that he's been here before — and "that fire had nothing to do with me... Well, a little bit!"

The two soon realise that something's horribly wrong. Where are those great sights — the Colosseum, the Circus Maximus, the Pantheon — that the Doctor never got to see? Why is there one hill, and not Rome's famous ... and why is it smoking? As a tremor rocks the streets, the Doctor realises they have arrived not in Rome, but in Pompeii in August 79 — "and it's volcano day!"

Sometime later, the Doctor and Donna meet up; he's learned the date from the locals, and it's exactly the day before the eruption; they got lucky that they didn't land then. The Doctor then tells her off when she tries to plan an evacuation. "Pompeii is a fixed point in history. What happens, happens. There is no stopping it." Donna tells the Doctor that she's going to have something to say about that; the Doctor tells her that he knows, given her personality. She follows him back to the TARDIS... but the Doctor's ship is gone! She rhetorically tells him to tell her that the TARDIS isn't gone; he literally complies. "Oi. Don't get clever in Latin!" Donna snaps at him. They find that the stallholder has sold it to local marble merchant, Caecilius, as a piece of "modern art".

Meanwhile, a red-hooded member of the Sibylline Sisterhood who has been following them reports to her fellow sisters and the High Priestess that the "blue box" has appeared in the marketplace. They find that this is a fulfilment of a Sibylline prophecy. However, it was to come at the time of fire, destruction and betrayal; clearly it is speaking of the next day, but what is this betrayal mentioned in the prophecy?

At Caecilius's house, his wife Metella is preparing their prophetically-gifted but sickly daughter Evelina for the arrival of the town's augur, Lucius Petrus Dextrus. Their son Quintus is also present; however, he is hungover from partying the previous night and has a bad headache. A tremor causes them to brace their valuables; apparently, this is common. Unable to catch one, they are lucky that the Doctor arrives and holds it in place. The family introduce themselves, and the Doctor uses his psychic paper to pass himself off as a marble inspector, which is also an excuse to get the TARDIS back. Both the Doctor and Donna assume the alias "Spartacus". Caecilius assumes they're married, which they deny; he then comes to the conclusion that they must be brother and sister as they DO look similar. The Doctor and Donna are surprised by this.

Lucius arrives, and the Doctor wins a verbal joust with the augur, earning praise in return for his cleverness. The Doctor then excuses himself and Donna, and they head to the TARDIS to leave. However, he is compelled to stay when he sees Caecilius unveil a marble plaque he has produced to Lucius' designs — it is recognisably an electrical circuit. Overhearing Lucius give prophecies, the Doctor tells Donna that they're in an age of "official superstition"; prophecies are the equivalent of ten o'clock news.

Overhearing them, Evelina tells her parents that they "use words like tricksters" and are mocking them. Seeing how ill Evelina is, the Doctor is told she breathes vapours for strength, but he disagrees that it is having that effect. She then asks if that's his opinion as a "Doctor". Lucius claims that Evelina's prophecies are easily faulted. However, when the Doctor says Lucius has been "out-soothsayed", the augur joins Evelina in predicting the truths about Donna and the Doctor. They see their real names, naming Gallifrey and London as their true homes, Gallifrey's destruction, and the Doctor's name being "written" in the stars of the Medusa Cascade. Evelina also states that his true name is not Doctor but is "hidden" and that he is a Lord of Time. Petrus Dextrus warns the Doctor "she" is returning and tells Donna that "there is something on your back". Evelina then faints.

Later, Donna helps Metella tend to Evelina; Metella sadly notes that Evelina is usually a sweet girl, but when the words of prophecy come through her, she is less kind. Donna wonders what's wrong with Evelina's arm, as there's a wrap around it; Metella explains that they bathe the injury in olive oil each night, but nothing has worked. Recalling Evelina said Donna came from far away, Metella asks her if she has seen the ailment before, undoing the wrap. To Donna's shock, the afflicted area is dark grey; feeling that part of Evelina's arm, Donna shockingly tells Metella that it's stone

Meanwhile, the Doctor is shown a hypocaust system powered by from Vesuvius itself by Caecilius, from which emit monstrous sounds from "the gods of the underworld". This system, he is told, was installed after the 62 earthquake on instructions from Lucius and the other soothsayers. The Doctor asks if that's when they started making sense; Caecilius admits that before the earthquake, soothsayers were less than accurate. However, since they started breathing in air from the hypocausts, they have predicted the future without a single flaw again and again. Curious, the Doctor asks if there have been any prophecies about tomorrow, to which Caecilius says there have not. The Doctor removes the vent and reaches into the hypocaust; it's filled with stone dust. "They're breathing in Vesuvius."

Finding Quintus lazing around, the Doctor asks him to show him where Lucius lives; however, he is ignored. Seeing he needs a new approach, the Doctor uses a magic trick to pull a gold coin from behind Quintus's ear, asking him again where Lucius lives. Quintus agrees to take the Doctor. They arrive outside Lucius's home, which the Doctor decides to break into. Climbing into a window, the Doctor helps Quintus in after him, since he has a torch to light the dim room. They find that not only is there the stone circuit that was made by Caecilius, but five others as well. Quintus is shocked by this, as Lucius claimed that Caecilius was the only person commissioned for the task. The Doctor explains that it's common practice for a criminal to acquire the required parts from different places to avoid suspicion.

Meanwhile, Evelina gives Donna a and talks about a teenager's life in Pompeii; however, Evelina says she's been promised to the Sisterhood for life. Donna wonders if Evelina gets a say in that, but Evelina has resigned herself to it as she has the gift of prophecy. Donna's hints about Vesuvius' impending eruption are ignored, and she realises that none of the seers have foreseen it. She tells Evelina about the eruption, which the sisterhood telepathically overhear through Evelina; Donna tells Evelina that even if she doesn't believe her about the danger, she should at least get her family to leave for a day. The sisterhood panic at the idea of a different prophecy. However, their High Priestess decries it as a false prophecy and to ignore the prophecies of their founder. She has seen a different vision, which is of an endless empire of Pompeii; she declares that Donna must be sacrificed. A tremor shakes the temple, which Surprina takes as the gods' approval.

Quintus and the Doctor, meanwhile, have been caught by Lucius. The Doctor helps him assemble the marble plaques into a circuit board. He asks who instructed Lucius to build this, saying he can help him. Dextrus takes this as an offence against the gods and threatens to have his guards kill them. The Doctor responds by trying to shake his hand — and breaks off Dextrus's completely petrified right arm. Using the sonic to shake the shelves, the Doctor knocks over the tablets, allowing himself and Quintus an opening to flee. Lucius inspects the carvings, finding not one of them is damaged; he begs the gods of the underworld to go after the Doctor and Quintus as they would prevent the rise of Pompeii. A safe distance from Lucius' home, the Doctor and Quintus hear thudding footsteps from underneath the ground.

Returning to Caecilius's house, they find Dextrus has summoned a giant, humanoid, stone-and-magma creature, which bursts up from the hypocaust. The Doctor tells Donna to get water, while he attempts to reason with the creature. Members of the Sisterhood appear behind Donna and drag her from the room. Only Evelina sees this, but one of the sisterhood motions to her to remain silent. Unable to reason with the creature, the Doctor has Quintus throw a bucket of water on it, causing it to harden and collapse into rubble. Noting that this was just a foot soldier, the Doctor notes its a good thing he stayed in Pompeii. Noticing that Donna isn't adding her usual quips to his theories, the Doctor notices she's missing.

At the altar in the sisterhood's temple, Donna has been tied down to a table as a sacrifice, though they cannot bind her considerable spirit. Just as Sister Spurrina lowers her knife — Donna's prattling voice will cease forever — the Doctor arrives, saying, "Oh, that'll be the day." Spurrina is aghast, saying no man can enter the Sybil's temple. Entering anyway, he tells them he had met the original Sibyl after whom the order is named, and she would be ashamed of them. Spreading the word with the blade of a knife? Spurrina moves to stab him, but the High Priestess demands to speak with the Doctor. With the curtain moved away, it is shown the High Priestess has been completely turned to stone. She confirms that it hurts, but the voices tell her it's necessary.

The Doctor realises that somehow, the people of Pompeii are turning to stone before the volcano erupts. The High Priestess sees into his mind and sees the image of an erupting volcano, demanding to know what a volcano is. Suspicious, the Doctor demands to know who she is; the High Priestess tells him, to which he says it's not her he's talking to. He's talking to the creature seeding itself into the human body through the lungs and turning it into a stone. The High Priestess says his logic is impossible, but the Doctor counters that by seeing into his mind like she's doing, she knows it's not. The alien, asserting control over the High Priestess, declares itself a Pyrovile; the sisters blindly begin chanting its name. The Doctor, taking a water pistol out of his jacket, warns her that he's "armed". He instructs Donna to open the hypocaust and demands to know what the Pyroviles are doing here.

The Pyrovile explains it is one of several aliens who crashed to Earth millennia earlier, awakened by the 62 earthquakes. Their adult form is the creature they saw at Caecilius' villa. They are a psychic race and have bonded with humans through the dust they breathe. The Doctor explains the psychics don't predict the future but can see through time. As he questions why the soothsayers can't see the volcano, Spurrina informs her sisters that she's looked into the Doctor's mind and knows the weapon is harmless. The Doctor confesses she's right but adds that it will sting. He fires a few squirts of water at the High Priestess, who wails in pain. Donna and the Doctor use the confusion to escape into the hypocaust, in towards Vesuvius itself.

Dextrus and the possessed high priestess each declare that their Pyrovile-induced prophecy of a Pompeiian empire must advance, the latter warning that the Doctor threatens their plans. As they run, Donna tries to convince the Doctor to stop Vesuvius's eruption. He again refuses, telling her the eruption is a fixed point in time which cannot be stopped or avoided. Donna asks him how he knows this as she is basically history to him as well, but he saved her and everyone else in 2008. The Doctor explains his Time Lord ability to see the past, present and all possible futures at once, calling it a burden. Donna presses him as to how many people died. The Doctor confirms the figure was about 20,000, and she asks him if it's alright to let all these people die. Before he can answer, they hear a roar, hinting that the Pyrovile are aware of their presence, forcing them deeper into the volcano.

Dextrus and the Cult of Vulcan take the circuit boards to the mountain; a Pyrovile arrives to take them. The Doctor and Donna, meanwhile, have reached the centre of the volcano. Inside it, they see what appears to be the remains of an escape pod, or something similar. Donna guesses that the aliens plan to blow up the mountain to launch themselves into space. However, the Doctor tells her they are planning something much more sinister. They are then discovered by Lucius, who summons the adult Pyrovile to hunt down Donna and the Doctor, declaring their presence a defilement to his masters' temple. The Doctor and Donna make their way towards the pod, briefly fending off an adult Pyrovile with the water-pistol. Reaching the pod, the Doctor politely asks Lucius as to the Pyroviles' plan before they die. Lucius announces that his masters' plan is to expand beyond Pompeii, to conquer the whole world. Donna points out that the Pyroviles could just go home, but Lucius retorts that their home planet, Pyrovillia, was "taken". Thus they will stay and conquer Earth, boiling its oceans and burning it to cinders.

The Doctor and Donna lock themselves in the Pyrovillian ship. Examining the controls, the Doctor finds the Pyrovile are using Vesuvius to set up a fusion matrix to convert millions of humans into Pyroviles. The matrix will bleed off so much of Vesuvius' pent-up energy there won't be enough to trigger the eruption — this is why the soothsayers have been unable to see it. There won't be an eruption anymore! The Doctor can switch off the Pyrovillian circuitry and save the world from conquest, but he will cause the eruption and the deaths of himself, Donna and twenty thousand people. And if Pompeii is destroyed, it's not just history... "it's me".

They choose the latter as the lesser of two evils, and, together, reverse the machine. Vesuvius roars into life, and both Lucius and the Pyroviles, at the centre of the explosion, are destroyed almost instantly. The explosion bursts through the top of the mountain as Vesuvius unleashes her fury. The residents of Pompeii watch in terror as ash falls upon them, thinking the sky is falling. Meanwhile, the Pyrovillian escape pod holding the Doctor and Donna is launched into the sky and lands between Vesuvius and Pompeii. The two run for the safety of the TARDIS. As they do, Donna tries to inform the citizens where it's safest to flee, but they ignore her in panic.

They reach the Caecilius family's home, where the Doctor ignores their pleas for help as Donna yells at him. With the TARDIS engines starting up, Donna is forced to board as well. As they dematerialise, Donna urges him to return and save the citizens. The Doctor refuses, saying if he could go back, he would — just as he would go back and prevent the destruction of Gallifrey, which also burned. After a moment of thought, Donna tearfully pleads with him — if not the city, then just save someone. Just one person! The Doctor relents and rematerialises the TARDIS inside the Caecilius home, where the family are huddled in a corner awaiting death. He offers them his hand and takes them into the safety of the TARDIS.

The Doctor, Donna, and the Caecilius family gloomily watch from the hills as the pyroclastic flows from Vesuvius destroy Pompeii. The Doctor explains why Evelina's visions have stopped — the massive explosion of Vesuvius caused a tiny rift in time that lead to the future where the Pyroviles won; however, now that future has been prevented, she can longer see the future. He promises that Pompeii will be remembered and found again one day. They then wonder who the Doctor is and why his "temple" has such size within. Caecilius, awed by the fury of Vesuvius, coins the word "volcano", but grieves for the people who are getting killed by the eruption. The Doctor and Donna leave, with him acknowledging that she was right "Sometimes I need someone".

Six months later — in early 80 — the Caecilius family has resettled in Rome. Lobus Caecilius has re-established his marble business, now worrying about a deal with the Egyptians that may set up his family for life. Evelina is a healthy and happy teenager once again, and is dating and wearing trendy outfits, much to her father's consternation. Quintus has been the most affected of the family — he is now training to be a doctor. He is told to give thanks to the household gods before he leaves for his studies. Doing so, Quintus smiles at the image of the gods and thanks them; the marble bas-relief shows the family's household gods to be the Doctor and Donna, and their temple the TARDIS.

Cast

 * The Doctor - David Tennant
 * Donna Noble - Catherine Tate
 * Stallholder - Phil Cornwell
 * Soothsayer - Karen Gillan
 * Spurrina - Sasha Behar
 * Thalina - Lorraine Burroughs
 * Caecilius - Peter Capaldi
 * Metella - Tracey Childs
 * Evelina - Francesca Fowler
 * Quintus - Francois Pandolfo
 * High Priestess - Victoria Wicks
 * Major Domo - Gerard Bell
 * Lucius - Phil Davis

Individuals

 * Donna mentions her father, Geoff Noble, only as "dad".
 * This is the second time the Doctor and Donna have been mistaken for a married couple in their time together.
 * Donna tries to rescue a child.

Religion

 * Evelina could have been a Vestal Virgin, had they moved to Rome.
 * Caecilius asks if Quintus has been cavorting with Etruscans and Christians at the thermopolium.

Foods and beverages

 * Caecilius orders ants in honey and a dormouse as a snack.

Locations

 * Donna thinks, at first that she's in Epcot when she sees a sign in English.
 * The Doctor tells Donna he visited Rome a long time ago and had no part in the Great Fire of Rome before adding, "Well, a little bit."
 * When seeing the future, Evelina mentions that the Doctor's name is hidden under the "Cascade of Medusa herself".
 * Gallifrey is mentioned by Lucius, and the Doctor is called a Lord of Time.
 * Lucius' villa is located on Foss Street.
 * When the Doctor mentions San Francisco, Caecilius thinks he is talking about a restaurant located in Naples.
 * The Doctor makes a pun about the Appian Way.

Organisations

 * The Doctor mentions the Shadow Proclamation when ordering a Pyrovile using a human host to reveal its species. He also asks for its home planet and galactic coordinates.

Time travel

 * The explosion of Pompeii caused a rift in time allowing an alternate timeline to seep backwards into the Pyrovillian alternative, creating visions.

Objects

 * The Doctor attacks the High Priestess and a mature Pyrovile with a cheap, plastic water pistol.
 * Donna sees a stall offering amphoras.

Story notes

 * Caecilius' purchase of the TARDIS in the belief that it's a work of modern art is a deliberate reference to City of Death — one of episode writer James Moran's favourite stories from the classic series. In City of Death, the TARDIS is parked in an art gallery, causing a pair of critics (John Cleese and Eleanor Bron) to discuss its artistic merits before being even more impressed when it dematerialises in front of them.
 * The Pyrovile were originally called Pyrovillaxians. This was shortened to Pyrovellians, then Pyrovile.
 * Originally The Fires of Pompeii was intended to be transmitted after Planet of the Ood, but this was swapped because, as Russell T Davies wrote in Doctor Who: The Writer's Tale:
 * "Since the Ood tale is surprisingly dark, I'd thought that it would undercut people's comedy expectations of Life With Donna, but then, at the read-through, I thought that the Ood episode was dark to the point of grim. It's a very macho, testosterone-fuelled script, and they're never my favourites, so, yes, it's better as the third episode."
 * BBC4 broadcast three related programmes on the same evening as the original broadcast; "Earth: the Power of the Planet" (an episode about volcanoes) at 2010BST, "Pompeii: the Last Day" at 2110BST, and "10 Things You Didn't Know About Volcanoes" (actually broadcast at 0155BST the following morning). The Radio Times listing for The Fires of Pompeii made reference to "Pompeii: the Last Day".
 * The fountain in this story is reused as the cloning vat in The Sontaran Stratagem.
 * In an email to Ben Cook in The Writer's Tale, Davies suggests that the escape pod the Doctor and Donna use to trigger the eruption and then flee Vesuvius might be a reworked Sontaran globe-ship, since they would need the ships for the upcoming Sontaran double episode. Whether or not they actually did so is unclear.
 * The "Petrus Dextrus" in Lucius Petrus Dextrus translates roughly to "stone right-hand". This is a reference to his right arm, which had turned to stone.
 * The name "Caecilius" translates roughly to "blind", which might be a reference to the people of Pompeii being "blind" about the upcoming eruption.
 * The names Caecilius, Metella and Quintus were taken from the historical character of, as well as his wife Metella and his son , all of whom featured in Book 1 of the Cambridge Latin Course, which is also set in Pompeii.
 * The Doctor jokes that Donna is from Barcelona, a reference to a running gag in Fawlty Towers. The Ninth and Tenth Doctors also talked of visiting the planet Barcelona with their companion. (TV: The Parting of the Ways and Born Again)
 * The Caecilius family scrambling to steady fragile valuables every time the house shakes is very similar to a bit from Mary Poppins, even down to the shouting of "Positions!"
 * The episode addresses a long-standing issue of the "gift of translation" the Doctor or the TARDIS bestows upon companions. It is revealed that while the Doctor and Donna hear the Romans speaking colloquial English, with Cockney accents in some cases, the Romans hear them speaking Latin. When Donna and the Doctor actually speak Latin phrases e.g. "Veni, vidi, vici", the Romans hear this as Celtic, as the English language hadn't yet developed. The Doctor seems to have been unaware of what would happen in such a case.
 * Discounting the Doctor Who TV movie (1996), which was filmed in Canada, and Daleks in Manhattan, which featured some second-unit photography in New York City but nothing involving the cast, this is the first regular-series episode to be filmed outside the UK since The Two Doctors, which was filmed in Spain in 1984.
 * This episode's events were deeply engraved in the Doctor's subconscious. So when he regenerated into the Twelfth Doctor, his subconscious chose the face of Caecilius to remind him to always try saving someone, no matter what the consequences were.
 * According to David Tennant on the episode commentary track, when the Doctor breaks off Lucius's arm, the original script had the Doctor throw it on the ground to break it into pieces. Tennant requested that this part be taken out, as he figured it was far too violent and destructive for the Doctor. Both him and Catherine Tate still consider the final cut to be "aggressive" by the Doctor's usual standards.

Ratings

 * 9.04 million viewers (UK final)

Studio

 * Upper Boat Studios, Treforrest
 * Cinecittà Studios, Rome

Location

 * Mount Vesuvius, Naples
 * Welsh Centre for International Affairs, Cardiff
 * Clearwell Caves, Gloucestershire
 * Morlais Quarry, Merthyr Tydfil
 * Taffs Well Quarry, Taffs Well

Production errors

 * Just before the Doctor finds out that everyone with the "gift" is breathing in Vesuvius, the Doctor's glasses fog up but in the next shot, they are all clear.
 * As the Doctor and Donna enter the TARDIS after watching the destruction of Pompeii from the hills, the front of the TARDIS is facing outward, towards the city. In the very next shot, showing a wide view of the surroundings, the TARDIS has rotated, as shown by the sign on the door now facing approximately 90° to the left. This is purely a CGI error, as the sound of the Doctor and Donna entering the TARDIS can be heard but not seen.
 * A major error is that once the Doctor breaks off Lucius Petrus Dextrus' right arm, he becomes wider and it is quite obvious by this that the actor's arm is strapped under his toga.
 * The word "BIRTVS" or "BURTVS" can be seen carved into the stone towards the end after the Doctor saved the family, more specifically when Evelina and Quintus are holding hands.

Continuity

 * The Doctor tells Donna that "that fire" had nothing to do with him. His first incarnation inspired Nero to begin the Great Fire of Rome when he accidentally set fire to a map of the new plan for Rome while visiting 64 AD. (TV: The Romans)
 * During the events of this story, there were two versions of the Doctor's seventh incarnation at large in the city involved in different adventures, one with Mel (which also involved in time-changing decisions), (AUDIO: The Fires of Vulcan) and another with Ace. (PROSE: The Algebra of Ice). The Tenth Doctor was presumably aware of this, which could also have been a reason behind his quick desire to depart.
 * The Doctor pulls the arm off one of his adversaries, just as he previously did with an Auton. (TV: Rose)
 * Dextrus says that Donna has "something on her back". (TV: Turn Left)
 * Dextrus says to the Doctor that "she" is returning, referencing Rose Tyler who would soon reunite with him. (TV: The Stolen Earth)
 * The Doctor's discussion of time and not interfering hearkens back to an argument that the First Doctor had with his companion Barbara Wright in Mexico in the 15th century. (TV: The Aztecs)
 * The Doctor produces a small spyglass from his pockets, much as he did in TV: Robot.
 * The Doctor also produces a water pistol, which would appear again (and be stolen by a Graske) in TV: Music of the Spheres.
 * The Doctor says it's volcano day, much as Jack did in TV: The Doctor Dances.
 * The destruction of Pompeii was later referenced by the Doctor when he wrestled with abandoning Bowie Base One in TV: The Waters of Mars.
 * The Doctor's TARDIS was previously mistaken for a work of art (TV: City of Death) and would be again. (PROSE: The War of Art)
 * Donna calls the Doctor "spaceman". (TV: The Runaway Bride)
 * The Doctor previously visited Rome in PROSE: The Stone Rose.
 * The Doctor would subconsciously base his twelfth incarnation on Lobus Caecilius' appearance. (TV: Deep Breath, The Girl Who Died)
 * Lucius mentions that Pyrovillia was lost, just as Cofelia said of the Adipose's breeding planet. (TV: Partners in Crime)
 * The Doctor later realises that it is one of the 27 planets stolen by the Daleks. It is returned by Donna Noble to its right position is space. (TV: The Stolen Earth/Journey's End)

Home video releases

 * This story was released in the Series 4 DVD box set in November 2008 along with the rest of the series.
 * It was also released as Series 4 Volume 1 in a vanilla edition with Partners in Crime and Planet of the Ood.