Year 1221 (MCCXXI) was a common year starting on Friday (link will display the full calendar) of the Julian calendar. Events <onlyinclude> By place Byzantine Empire November – Emperor Theodore I (Laskaris) dies after a 16-year reign and is succeeded by his son-in-law John III (Doukas). John fends off Theodore's brothers, who believe that they have the better claim for the throne of the Empire of Nicaea. In December, he becomes the sole ruler, and during his reign, the Empire becomes the most powerful of the Byzantine successor states and the frontrunner in the race to recover Constantinople from the Latin Empire. John also cultivates a close relationship with Emperor Frederick II and negotiates with Pope Honorius III about the possibility of reuniting the Church. Fifth Crusade June – Sultan Al-Kamil again offers peace terms to Cardinal Pelagius with the cession of Jerusalem and all Palestine apart from Oultrejordain, together with a 30 years' truce and money compensation for the dismantling of Jerusalem. Meanwhile, a German contingent under Louis I of Bavaria arrives at Damietta, with orders from Frederick II not to launch an attack on Cairo until the emperor's arrival. Louis and Pelagius decide to advance into Egypt towards Mansoura, where Al-Kamil has built a fortress to protect Cairo. The Crusaders assemble their armies and tents are set up just up the Nile, on June 29. July 4 – Pelagius orders a three-days fast in preparation for the advance. King John I of Jerusalem arrives at Damietta, to rejoin the Crusade at the command of Honorius III. The Crusader force moves towards Sheremsah, halfway between Faraskur and Mansoura on the east bank of the Nile, occupying the city on July 12. Sources tell of 630 ships of various sizes, 5,000 knights, 4,000 archers, and 40,000 men. A horde of pilgrims march with the army. They are ordered to keep close to the river, to supply the Crusaders with water. Pelagius plans a new offensive and leaves a large garrison at Damietta. July 24 – Pelagius moves the Crusader forces near Ashmun al-Rumman, on the opposite bank from Mansoura. Queen-Regent Alice of Cyprus and leaders of the military orders warn Pelagius of a large Muslim army being formed in Syria. Meanwhile, the Egyptian army under Al-Kamil crosses the Nile near Lake Manzaleh and establishes themselves between the Crusader camp and Damietta. In the Ushmum canal at Sheremsah, Al-Kamil's ships sail