9th century

The 9th century was when the Doctor liked to get his milk. According to the Tenth Doctor, he went to "nice little farm" in France, at least until the milkmaid developed boils on her hands. (COMIC: Wrath of the Warrior)

At some point in the century, the Second Doctor, Ben and Polly arrived in Baghdad, having been chased there by the Cat-People. (PROSE: Invasion of the Cat-People) The Library of St John the Beheaded was founded sometime this century. (PROSE: All-Consuming Fire) The Fifth Doctor and Amy visited Sudan in this century in search of the fifth segment of the Key to Time. (AUDIO: The Destroyer of Delights)

This century also saw the death of Ashildr, a Viking girl who was brought back to life by the Twelfth Doctor, accompanied by Clara Oswald, through a Mire repair kit, having gave her life to repel a Mire attack on her village. As the kit would never stop repairing her, Ashildr was rendered effectively immortal. (TV: The Girl Who Died) She would thus live beyond well beyond the average lifespan of a human, to the end of the universe. (TV: Hell Bent)

The Flood was sealed in a glacier on Mars by the Ice Warriors in this century. (COMIC: The Wolves of Winter)

It was in this century that a reconnaissance scout Dalek arrived on Earth, becoming possibly the first Dalek to ever arrive on the planet. It was met with the force of a human army and the Battle of Hope Valley ensued. When the humans won the battle, three custodians were trusted to hide the separated parts of the Dalek in the farthest corners of the Earth. The Third Custodian was shot by bandits on his journey across a valley that would later become Sheffield. (TV: Resolution)

The Varangians were 9th century Russian Vikings. Kate Wilson believed that they sounded like something out of Star Trek. (AUDIO: The Conspiracy)

Behind the scenes
Although not stated in The Girl Who Died, the television story The Woman Who Lived, set in 1651, has Ashildr mentioning that she had 800 years of adventure, placing the former around this century.