Fourth Crusade: Despite letters from Pope Innocent III forbidding it and threatening excommunication, Catholic crusaders begin a siege of Zara (now Zadar, Croatia).

The Fourth Crusade (1202–1204) was a Latin Christian armed expedition called by Pope Innocent III. The stated intent of the expedition was to recapture the Muslim-controlled city of Jerusalem, by first defeating the powerful Egyptian Ayyubid Sultanate. However, a sequence of economic and political events culminated in the Crusader army's 1202 siege of Zara and the 1204 sack of Constantinople, rather than the conquest of Egypt as originally planned. This led to the partition of the Byzantine Empire by the Crusaders and their Venetian allies, leading to a period known as the Frankokratia.