It is often stated that the sea is central, in more ways than one, to our understanding of the Mediterranean World, particularly in Antiquity. At the heart of this lie the unprecedented levels of maritime connectivity between people and cultures afforded by the sea and the ships and boats that plied the waters of the ancient world. Our understanding of those vessels has been greatly expanded in the last half a century through a wealth of archaeological evidence that has allowed a detailed understanding to be developed of the construction of such vessels, the goods and products of trade and the trade routes themselves. By contrast, the archaeological remains of the rigging and sails by which such vessels were used in antiquity has received less attention. However, these remains, in conjunction with the rich iconographic and literary sources can paint a detailed picture of the nature of seafaring in the ancient Mediterranean, including an understanding of the potential performance of such sailing vessels. For the most part, the mariners of the ancient Mediterranean utilized a square-sail that we can identify as having a specifically Mediterranean tradition of use. This lecture addresses how maritime archaeologists have understood the practical aspects of sailing in the ancient Mediterranean in the past and highlights and discusses a number of key elements that are not currently widely understood. This includes the development of the sail itself, the evidence for whether or not ancient mariners could sail to windward. Finally, it is possible to address the eventual disappearance of the Mediterranean square-sail altogether and its replacement with the lateen sail during the late-antique and early medieval period.