Were Medieval Seamen Aware of Mediterranean Currents?

Medieval seagoing vessels were propelled by either sails or oars, or sometimes both. Therefore, the influence of powerful sea currents, such as those prevailing though the Straits of Gibraltar and Messina, would have been of prime importance to medieval sailors, and the crusaders in particular. However, local currents were often affected by winds, and unless local knowledge was involved, were not known to seamen without the means to measure them. Courses sailed by some famous travellers such as Saewulf or Ibn Jubayr are described, showing that minor currents were disregarded. It is suggested that, except for the well-known currents, other minor water movements were not considered by medieval sailors in plotting their courses.