

Unfortunately, this was the city that Martin Septim was in and he had to be rescued by the player. You the player were with the emperor and before he was killed he told you that he had another son Martin Septim, (after the death of the emperor gates to the realm of Oblivion opened) and the daedra attacked and destroyed the city of Kvatch in a deadly surprise attack. This crisis was caused by the Mythic Dawn Cult, worshipers of Mehrunes Dagon, who assassinated emperor Uriel Septim VII and his sons. The planes of Oblivion (ruled ultimately by Mehrunes Dagon) open and an onslaught of daedra attempt to take over the province of Cyrodiil, known as the Oblivion Crisis.

The fourth Elder Scrolls game set after The Elder Scrolls III: Morrowind.
