The bell tower is separate from the cathedral and dates back to the 10th century. It is thought to have originally been a watchtower.
It's nice to make the short drive inland to Ruvo on a hot summer's evening and take a walk through the quiet streets of the historic center. Ruvo sits on a slight rise, 260 m above sea level, and the air is always several degrees cooler than in Molfetta.
(These are cell-phone photos, so the quality is not the best...)