Alaaddin Mosque is on the top of the so-called Alaaddin Mound (Alaattin Tepesi). The Palace of the Seljukid sultans was once inside a citadel that was standing on this small hill. The Alaaddin Mosque was built adjacent to the palace following the example of Early Islamic palace mosques. The mosque comprises two different structural units juxtaposed in different periods. The east wing of the building is believed to have been built by Sultan Mas'ud before 1155. There is a trapezoidal interior filled with rows of Hellenistic and Byzantine columns, tied together by pointed arches that run parallel to the mihrab wall. The west wing, on the other hand is known to have been built during the first quarter of the thirteenth century by the Sultans Izzeddin Keykavus and Alaaddin Keykubad. At the centre of this wing, there is a domed bay in front of the mihrab. According to Aptullah Kuran, this masjid was, in all probability, the private masjid of the Seljukid royal palace, and it must have been combined with Mas'ud's Old Mosque during the fourteenth century. There are two polygonal tombs (kumbet) in the courtyard, which were built for the members of the Seljukid dynasty.