Fall of Arcadia

The Fall of Arcadia was a battle fought on the last day of the Last Great Time War. The city of Arcadia was thought to be "the safest place on Gallifrey", because it was protected by 400 sky trenches. Despite this, a massive Dalek force managed to penetrate the trenches and swarmed over the city, exterminating Time Lord soldiers and civilians alike. (TV: The Last Day, The Day of the Doctor)

The Doctor was at Arcadia, fighting on the front lines. (COMIC: The Forgotten) Witnessing the devastation, he blasted the words "NO MORE" into a wall as a message to both the Daleks and the Time Lords, and departed to steal the Moment with the intention of ending the war once and for all. (TV: The Day of the Doctor) When he mentioned the battle to Rose Tyler in his tenth incarnation, he still hadn't mentally recovered. (TV: Doomsday)

Behind the scenes
According to Doctor Who: The Encyclopedia, the Doctor watched as the Daleks fled from the planet.