Thal-Dalek battle

The Thal-Dalek battle, (AUDIO: Return to Skaro) also known as the Great Siege (AUDIO: Masters of War) and, to the Time Lords, the "Dead Planet Incident", (PROSE: Dalek Combat Training Manual) was a defining confrontation in the conflict between the Thals and the Daleks on the planet Skaro. While important to Skaro's history, the battle was of much greater significance as the event in which the Doctor first encountered the Dalek race. (TV: The Daleks) For the First Doctor, this first encounter with the Daleks was vital for his growth, proving to him that, to be "the Doctor," he needed to fight evils like the Daleks. (TV: Into the Dalek)

Dating
Explaining how the Daleks could have invaded 22nd century Earth, the First Doctor claimed to Ian Chesterton that the Thal battle and the demise of the Daleks they had witnessed earlier took place a million years in the future, and that the current Earth invasion was their "middle history". (TV: The Dalek Invasion of Earth) However, he also came to realise the Daleks likely had other cities on Skaro, meaning that the invasion likely came after the Thal-Dalek battle, (PROSE: Doctor Who and the Dalek Invasion of Earth) with most accounts indeed claiming that the Dalek invasion of Earth came after the Thal-Dalek battle. (PROSE: The Whoniverse, Dalek Combat Training Manual, et. al)

During the Last Great Time War, a field report the Time Lords' Dalek Combat Training Manual pinpointed the incident's temporal co-ordinates to the 20th century, the native century of the Doctor's human companions at the time. However, this was contradicted by their timeline of Dalek activity in linear history, which placed the Thals' triumph over the Daleks in the 22nd century, preceding the Moroks acquisition of a Dalek casing and the invasion of Earth; at the same time, the Earth invasion was indicated to precede the Dead Pllanet Incident in the Daleks' timeline. Furthermore, some Gallifreyan theorists pondered whether it was possible that this battle occurred near the end of the Daleks' timeline after some kind of event forced them to abandon conquest and flee back to Skaro, (PROSE: Dalek Combat Training Manual) but most accounts held that the battle was early in Dalek history, with their first encounter with Doctor showcasing that life existed on other worlds, thus marking the battle as the founding point for the idea of the universe-wide Dalek Empire. (AUDIO: The Lights of Skaro)

One account suggested that it took place in or around January 2064, or eighteen months prior to 31 July 2065. (PROSE: Peaceful Thals Ambushed!)

Origins
Whilst the Thals had been all but wiped out when their city was attacked by the first Daleks created by Davros, (TV: Genesis of the Daleks) a tribe of survivors was founded by Bettan, a Thal soldier who had met the Fourth Doctor on his mission to interfere with the Daleks' development. (PROSE: The History of the Daleks) In the centuries following the Thousand Year War, (TV: Genesis of the Daleks) the Thals became pacifists, unwilling to risk another destructive war on Skaro. For years, they struggled to survive in the planet's hostile environment and were threatened with starvation. There only source of hope lay inside the Dalek City, and with their old enemies, the Daleks. Many Thals distrusted them but others, in the Thals' desperate situation, were willing to believe the Daleks may have changed just as they themselves had. Ultimately, the Daleks had not changed and still feared and hated the Thals as much as ever. (TV: The Daleks)

At some point, one group of Thals embarked on a dangerous quest to find the ruins of the Thal Dome and resettle. Some of the party believed the Daleks were long dead. Just two Thals survived the journey and reached the Dome ruins, only to discover it had already been occupied by the Daleks. The two survivors were exterminated. (COMIC: Safe Haven)

Entering the city
The First Doctor, Susan, Ian Chesterton and Barbara Wright first arrived on Skaro in the petrified jungle. They were captured and imprisoned by the Daleks while exploring the city. The Daleks briefly allowed Susan to return to the TARDIS, where she made contact with Alydon of the Thals and befriended him. After learning of this, the Daleks had her write a message intended to lure the Thals into the city with the promise of food, so they could be killed. To save the Thals, the Doctor and his companions broke out of their prison cell and escaped the city, destroying a few Daleks along the way. Ian stayed behind as the Thals entered the city and warned them of the trap, but not before the Thal leader, Temmosus, was killed by the Daleks. (TV: The Daleks)

Retaliation
During their imprisonment, the time travellers had lost the TARDIS's fluid link to the Daleks, and were stranded on Skaro until it was recovered. They had disagreements over the moral question about whether the Thals should help them recover it. They were able, however, to convince the Thals that their own survival was worth fighting for. Alydon, as new Thal leader, rallied his people to fight.

Meanwhile, the Daleks had also recovered some of the Thals' anti-radiation drugs. Several Daleks died after testing the drugs, leaving the rest to conclude that they needed radiation to survive. They began planning to detonate another neutron bomb to increase the radiation levels on the planet, and wipe out the Thals in the process. (TV: The Daleks)

Attack on the city
The Thals divided their forces to perform a two-pronged attack on the city. Ian, Barbara, Elyon, Kristas, Ganatus, and Antodus ventured through the Drammankin Mountains via the Lake of Mutations, although Elyon and Antodus did not survive. The rest of the Thals disrupted the Daleks' video and radio equipment, but in the process, the Doctor and Susan were captured again.

Both bands entered the city as the Daleks began the countdown to the detonation and attacked the Daleks head-on, with both sides suffering casualties. (TV: The Daleks) Earth's Space News Agency had been monitoring the planet Skaro from afar using the hyper-space video-phone (COMIC: Power Play) and the BBC was subsequently able to report on the Daleks' ambush of the Thals while the battle was still ongoing. (PROSE: Peaceful Thals Ambushed!)

In the end, the Thals cut the power supply to the city, deactivating the Daleks. (TV: The Daleks) As Ian also recounted, the Thals hacked to bits the glass casing housing the Dalek leader. (PROSE: Doctor Who in an Exciting Adventure with the Daleks) However, not all the Daleks were destroyed. The autonomic safety protocols of the city's subterranean incubation level sealed it off, protecting the ruling Dalek Supreme and the embryo Daleks. Without any operating Daleks to operate the incubation level's systems however, the Daleks residing in it went into a state of suspended animation. They would go on to spend decades in this environment, overcoming their dependency to radiation in the process. (AUDIO: Return to Skaro)

Aftermath
With the Dalek City now under their control, the Doctor suggested the Thals move in. It contained food and technologies such as artificial sunlight which would help the Thals with agriculture. (TV: The Daleks) Ian also recalled that the Thals threw a celebratory feast. (PROSE: Doctor Who in an Exciting Adventure with the Daleks)

In the immediate aftermath of the battle, Ace misued an omega device when she attempted to time lock Skaro, the shifting of the planet's timeline depositing Bernice Summerfield and several others in the abandoned Dalek City. When they inadvertently reactivated the city's power systems, a Dalek came online. The lone Dalek attempted to continue the plan to further irradiate the atmosphere only for Bernice and the Seventh Doctor to summon its future self to it. Horrified that its future counterpart had abandoned the goal of leaving its casing, the two versions of the Dalek opened fire on each other, restoring the natural flow of time on Skaro and leaving the city dead once again. (AUDIO: The Lights of Skaro)

Alydon became High Leader of the Thals and married Dyoni. Succeeding generations of Thals were told the story of the battle and the part played by the Doctor and his companions, who quickly passed into Thal legend. Ultimately, the Thals chose to not to inhabit the Dalek City and constructed the Thal City instead. The Dalek City was placed off-limits to all but scientific research teams and vegetation eventually reclaimed much of it in the ensuing fifty cycles. (AUDIO: Return to Skaro)

Reprisal
Unknown to all but the Thals' chief scientist, Tryana, the Thal City was built with the cooperation of the Dalek Supreme and the surviving Daleks. After encountering her during one of her surveys of the Dalek City, the Dalek Supreme manipulated her into believing they could help rebuild Skaro. In particular, they helped Tryana build ionisation towers to clear the radiation from the atmosphere. In return, Tryana provided them with power from the Thal City and kept their presence a secret.

When the time was right, the Daleks hijacked the towers and used them to attack the Thals in their own streets, in advance of a new Dalek army invading the city. With the return of the Doctor to Skaro, the Thals regained control of the towers and drove the Daleks back to their city. The Dalek Supreme ordered a second assault on the weakened Thals but Ian helped them overload the power feeding into the Dalek City. The excess of power destroyed the Daleks and much of the city. The Thals resolved to be more vigilant in the future and continue to defend their city. They worried that the Daleks still survived in other settlements elsewhere on Skaro. (AUDIO: Return to Skaro)

Legacy
The legend of the Doctor persisted in Thal culture into the 26th century, to the eve of the Second Dalek War. Abandoning their apathetic pacifism, the Thals continued to fight the Daleks on other planets. However, the Third Doctor warned Taron's party on Spiridon not to romanticise the conflict, lest the Thal culture revert to the opposite extreme leading them to develop a lust for war that would do more harm than good. (TV: Planet of the Daleks) Indeed, some Thals eventually did became more aggressive like their ancestors during the time of the Kaleds. Delani was a Thal commander responsible for the destruction of Terakis, sacrificing its native species in order to destroy the Dalek Eighth Fleet. (PROSE: War of the Daleks)

One of the Daleks involved in the First Doctor's first encounter with its kind may have been the Dalek to later take on the title "Dalek Prime Strategist". (PROSE: The Restoration Empire) Using their Mind Analysis Machine to forcibly ascertain the Third Doctor's identity during the Time Paradox Incident, the Daleks saw the face of the First Doctor, "as [they] knew him on Skaro." Soon after, the Doctor told them that, as he had defeated them on Skaro, he would defeat them on Earth too. (PROSE: Doctor Who and the Day of the Daleks)

Eighteen months after the battle, a theatrical Technicolor film entitled Dr. Who and the Daleks was released on Earth in cinemas. It contained a fictionalised account of the Dalek ambush and of the subsequent battle. (PROSE: Peaceful Thals Ambushed!)

After the two encounters with the Daleks on Skaro, (TV: The Daleks, AUDIO: Return to Skaro) the Doctor later encountered the Daleks again when they invaded Earth during the 22nd century. (TV: The Dalek Invasion of Earth) Its failure led the Daleks to recognise who the Doctor was, beginning a deadly rivalry spanning all of space and time (TV: The Chase, et al.) with massive consequences for the Daleks, Time Lords and the universe as a whole. (TV: Genesis of the Daleks, The Day of the Doctor, Dalek, The Parting of the Ways, et al) Yet the Twelfth Doctor considered that his original encounter with the Daleks changed his outlook on life for the better, by showing him that "the Doctor was not the Daleks." (TV: Into the Dalek)

The Dalek City itself became the site of future conflicts. Surviving Daleks within were briefly revived by human explorers who landed on Skaro, but they were deactivated once more. (AUDIO: The Curse of the Daleks) The Daleks later reclaimed and rebuilt the city. The Dalek Emperor resided within but it was devastated by an internal rebellion instigated by the Second Doctor. (TV: The Evil of the Daleks) The Dalek Prime later instigated another similar rebellion to weed out Davros' supporters so the Imperial-Renegade Dalek Civil War could be brought to an end. (PROSE: War of the Daleks)

According to Davros, the Daleks maintained a strong concept of home. Following the Last Great Time War, they returned to Skaro and rebuilt the Dalek City yet again, housing their dying creator. It was largely devastated once more after the Doctor's regeneration energy revived the dead Dalek mutants which swarmed the city. (TV: The Magician's Apprentice/The Witch's Familiar)

Though there existed multiple accounts of the Thal-Dalek battle, all of them agreed that Ian Chesterton had been the one who rallied the Thals against the Daleks. When the Time Lords sought to rally the Sensorites against the Daleks, they recruited Ian based on his previous success. (AUDIO: Sphere of Influence) The Thal-Dalek battle was among the many encounters with the Daleks and the Doctor that the Eleventh General compiled for the Time Lord army in the Last Great Time War to study. Upon studying the battle, and being unable to find records of other Daleks being so heavily reliant on static electricity, some Time Lords theorised, like the First Doctor had, that the battle had actually taken place near the end of Dalek history, after some great tragedy had caused the collapse of the Dalek Empire. (PROSE: Dalek Combat Training Manual)

In the post-Time War universe, this incident was covered as a part of known Dalek history in The Dalek Conquests, a documentary which was itself produced following the Van Statten Incident on Earth in 2012. (AUDIO: The Dalek Conquests)

Parallel universes
In the Unbound Universe, the Thal-Dalek battle was remembered by the races of Skaro as the Great Siege. Though the Doctor and the Thals had initially believed this to be the end of the Daleks, those who had been off-world at the time of Siege returned to reclaim Skaro. (AUDIO: Masters of War)

Behind the scenes

 * The Discontinuity Guide maintained that the First Doctor's claim of the battle being a million years in the future was pure and inaccurate speculation. According to The Discontinuity Guide, the Daleks in the battle were early products of the experimental program conducted by the late Davros and had been left behind on Skaro whilst more advanced Daleks had taken to space. These primitive Daleks were all wiped out in the battle with the Thals, though the advanced Daleks would later return to make their home on Skaro, preceding the Dalek Civil War which took place somewhere between the 19th century and the mid-22nd century. It is further noted that, since the Fourth Doctor inadvertently changed Dalek history so that Davros survived, this event would have occurred vastly differently if it happened at all in the new timeline.
 * As recounted by Susan in NOTVALID: Whatever Happened to Susan Foreman?, the battle did indeed take place, as the First Doctor had claimed, in the distant future relative to the 22nd century Dalek invasion, which had been waged by Daleks who, having been defeated on Skaro by the Thals led by Ian, used their own TARDIS to travel into the past with the intent to wreck revenge on Ian's people or, better still, prevent Ian himself from being born. However, they were unable to go any further back than 2164 due to a leak in their fluid link.
 * The Dalek Handbook dates the events of The Daleks as taking place in 1963, operating on the assumption that the Doctor returned Ian and Barbara to the right time after An Unearthly Child but not the right place. The Dalek Combat Training Manual hints at but not does explicitly reiterate this by placing the event in the 20th century.
 * An alternative account of the Thal-Dalek battle is given in the film Dr. Who and the Daleks.
 * In DWM 206's Doctor Who? instalment, the prelude to the battle is explicitly named as the "Decoy Food Ambush of 1963". Thirty years later, in the 1990s, a policeman arrests the entire Dalek race for their parts in the murder of Thal 306 during the ambush.
 * Lance Parkin's reference guide AHistory, which presupposed that the War in Heaven was the same as, or another facet of, the Last Great Time War, defined the Doctor's first encounter with the Daleks as Last Contact, the event in which the enemy destined to destroy Gallifrey would become known and the War would become inevitable.