We have used the general term 'secondary sources' to indicate everything that represents, refers to or describes one of the countless aspects of the study of naval history. These materials include archived documents that, in most cases, refer to boats and ships indirectly for their political, juridical, economic and military implications.

Other more important sources, which are much rarer, are the actual technical descriptions of boats and ships, including the manuscripts relating to naval architecture that were compiled by the shipyard foremen or boatbuilders to describe, compare and advertise their creations.

Lastly, any type of depiction or pictorial representation: construction plans, sculptures, miniatures, frescos, paintings ad engravings, votive tablets and models. Each of these, even when the images are naive or stylized, can reveal important details about boats, ships and their crew; in fact they are often the only remaining testimonies to the existence of many types of ships.