Abbasid Baghdad had a large polo ground outside its walls, and one of the city's early 13th century gates, the Bab al Halba, was named after these nearby polo grounds. The game continued to be supported by Mongol rulers of Persia in the 13th century, as well as under the Safavid dynasty. In the 17th century, Naqsh-i Jahan Square in Isfahan was built as a polo field by King Abbas I. The game was also learnt by the neighbouring Byzantine Empire at an early date. A "tzykanisterion" (stadium for playing "tzykanion", the Byzantine name for polo) was built by emperor Theodosius II (r. 408–450) inside the Great Palace of Constantinople. Emperor Basil I (r. 867–886) excelled at it; Emperor Alexander (r. 912–913) died from exhaustion while playing and John I of Trebizond (r. 1235–1238) died from a fatal injury during a game.