Year 1256 (MCCLVI) was a leap year starting on Saturday (link will display the full calendar) of the Julian calendar. Events By place Mongol Empire Spring – Mongol forces (some 80,000 men), under Hulagu Khan, cross the Oxus River, and begin their campaign to destroy the remaining Muslim states in southwestern Asia – with the first objectives being the Nizari Ismaili strongholds and Baghdad, the capital of the Abbasid Caliphate. The roads across Turkestan and Persia are repaired, and bridges built. Carts are requisitioned to bring siege machines from China. October – Mongol forces led by Baiju Noyan (operating under Hulagu Khan's command) win a victory over Kaykaus II, Seljuk ruler of the Sultanate of Rum, and capture Anatolia. Kaykaus flees to the Byzantine court where he seeks refuge at Constantinople. The Empire of Trebizond fearing a potential punitive Mongol expedition, becomes a vassal state and is forced to pay a tribute tax every year in gold and silk. November 8–23 – Siege of Maymun-Diz: Mongol forces under Hulagu Khan successfully besiege the mountain castle of Maymun-Diz. Hulagu encircles the fortress and begins a bombardment for three days by mangonels from a nearby hilltop. On November 19, Nizari Isma'ili imam Rukn al-Din Khurshah surrenders, but a small part of the garrison refuses and fights a last stand, until they are killed after three days. December 15 – Mongol forces under Hulagu Khan capture and dismantle Alamut Castle (near the Masoudabad region) after the surrender of the Nizari Ismaili leaders. Hulagu founds the Ilkhanate dynasty of Persia, which becomes one of the four main divisions of the Mongol Empire. The Nizari Ismaili government is disestablished, some of them migrate to Afghanistan, Badakhshan and Sindh (modern Pakistan). Europe War of the Euboeote Succession: Achaean forces under William II of Villehardouin attempt to gain control of the island of Euboea, which is resisted by the local Lombard barons (or "triarchs") with the aid of the Republic of Venice. Wiilliam launches devastating raids in Euboea. Guy I de la Roche, the "Great Lord" of Athens and Thebes, enters the war against William, along with other barons of Central Greece. British Isles Prince Llywelyn ap Gruffudd invades the northern coastal areas that have agreed to English rule (see 1254). Edward (the Lord Edward), who has been given the areas to govern himself by his father, King Henry III, asks him for support but Henry refuses.