South of the Il-Arslan Mausoleum lies the base of the Mamun II Minaret, which was built in 1011. It was reduced to a stump by the Mongols, rebuilt in the 14th century and finally toppled by an earthquake in 1895. Nearby you'll see the so-called 'portal of an unknown building', sometimes also referred to as the Gate of the Caravanserai. The structure is now thought to have been the entrance to the palace of Mohammed Khorezmshah, due to its ornateness and the thickness of its walls.