At the beginning of the Fifth Crusade, it was agreed that a force would attempt to take Damietta, located at the mouth of the river Nile.

The Crusaders then planned to use this city as a launching point for the southern portion of a pincer attack upon Jerusalem from Acre and Suez.

The first objective of the Crusaders was to take the defensive river tower that protected the fortress of Damietta and anchored one end of a chain across the harbor.

[2] The use of this remarkable siege engine aided the Crusaders in taking the tower, and opening the way for the fleet to attack the fortress.

In September, Cardinal Pelagius, Bishop of Albano and Legate of the Apostolic See arrived at the Crusader camp and proceeded to challenge the command of John of Brienne, King of Jerusalem, claiming that the Church held greater authority than a secular leader.

The Crusaders quickly advanced, occupying the city of Tinnis, and spent the spring and summer fighting the Muslim troops with varying success.

On August 29, the Crusaders attempted a large-scale attack on the enemy camp, but they quickly became disorganized and the Sultan's counterattack was fairly successful.

The terms were highly favourable to the Crusaders; the Muslim leaders had agreed to surrender the city and kingdom of Jerusalem, the Holy Cross, and all Christian captives in Egypt and Damascus, only withholding the fortresses of Kerak and Montreal.

The exact numbers are unclear, but out of the 60,000–80,000 inhabitants prior to the beginning of the siege, less than 10,000 remained alive; some sources recount as few as 3,000 left.