The Sacking of Coruscant was the last battle of the Great War in 3653 BBY.
While the talks were ongoing, an elite Sith army infiltrated Coruscant and immediately began attacking important structures, including the Jedi Temple. Six Jedi Council members were killed as Sith warships pummeled the world with turbolaser fire. The Jedi Temple was eventually destroyed and the world was in ruins.
The battle forced the Republic to sign the embarrassing Treaty of Coruscant.