and included moving around counters representing soldiers, with 'custodian' captures made by getting one of the adversary's pieces between two of one's own. After the Muslim conquest of Persia (638–651) Shatranj spread to the Arab world. While pre-Islamic chess sets represented Elephants, Horses, Kings and Soldiers; the Islamic prohibition against image worship led to increasing abstraction in chess set design. Islamic chess pieces were therefore simple cylindrical and rectangular shapes. The game became immensely popular during Abbasid Caliphate of the 9th century. The Abbasid Caliphs Harun al-Rashid and Al-Ma'mun were avid Shatranj players. During this period Muslim chess players published several treatises on chess problems (mansubat) and chess openings (ta'biyat). Elite players such as Al-Adli, al-Suli and Ar-Razi were called aliyat or "grandees" and played at the courts of the Caliphs and wrote about the game. Al-Adli (800–870) is known for writing Kitab ash-shatranj (book of chess), a comprehensive work on the game, including history, openings, endgames and chess problems. Al-Adli also developed a system for ranking players. During the reign of the Turko-Mongol conqueror Timur (1336–1405), a variant of chess known as Tamerlane chess was developed which some sources attribute to Timur himself who was known to be a fan of the game. Various games in the Tables family were also quite popular and are known as ifranjiah in Arabic (meaning "Frankish") and as Nard in Iran. Many of the early Arabic texts which refer to these games often debate the legality and morality of playing them. This debate was settled by the eighth century when all four Muslim schools of jurisprudence declared them to be Haraam (forbidden), however they are still played today in many Arab countries. Other popular games included Mancala and Tâb. Polo (Persian: chawgan, Arabic: sawlajan) was first played in Sassanid Persia. It passed from Sassanid Persia to the neighboring Byzantine Empire at an early date, and a Tzykanisterion (stadium for playing polo) was built by emperor Theodosius II (r. 408–450) inside the Great Palace of Constantinople. After the Muslim conquests, it passed to the Ayyubid and Mameluke dynasties, whose elites favored it above all other sports. Notable sultans such as Saladin and Baybars were known to play it and encourage it in their court. Playing cards were imported from Asia and India and were popular during Mamluk dynasty Egypt, featuring polo sticks, coins, swords, and cups as suits. Gallery India India saw a number