The great tower of Qalawun, which had both a defensive function and an ostentatiously visual vocation, dominated the castle’s southern face.

By building this tower, Qalawun killed two birds with one stone: he strengthened the side likely to face attack, and positioned himself alongside Baybars as a hammer of the Crusaders in the Near East, as indicated by a monumental inscription along the entire face of the tower.

"In the name of Allah... This tower of good omen was rebuilt during the days of our master the august sultan, the lord, the scholar, the just, assisted by God, defender of the faith, the warrior, the fighter, the defender of the frontiers, the victorious, al-Malik al-Mansur Saif al-dunya wal-Din Qala un al-Salihi, the associate of the emir of the believers, may God grant him eternal life and lend him support! It was constructed in the year 684 (1285)” .

The south tower is a large quadrangular structure nearly 17 metres wide and 20 metres deep. Solid at its base, it has an upper room with casemates organised around a large central pillar.

The tower has an obvious military purpose: it projects 15 metres beyond the curtain wall, and has nine arrow slits positioned over three sides, and a double-level defensive crown composed of a stone corbelled gallery on a continuous machicolation, and a wall-walk behind a crenelated parapet. A postern opens at the foot of the tower on its left face. A passage then connects the ditch to the castle and stables behind.