Periplus is the Latinization of an ancient Greek word, περίπλους (periplous, contracted from periploos), literally "a sailing-around." Both segments, peri- and -plous, were independently productive: the ancient Greek speaker understood the word in its literal sense; however, it developed a few specialized meanings, one of which became a standard term in the ancient navigation of Phoenicians, Greeks, and Romans.
A periplus was a manuscript document that listed, in order, the ports and coastal landmarks, with approximate intervening distances, that the captain of a vessel could expect to find along a shore. It served the same purpose as the later Roman itinerarium of road stops; however, the Greek navigators added various notes, which if they were professional geographers (as many were) became part of their own additions to Greek geography. In that sense the periplus was a type of log.
The form of the periplus is at least as old as the earliest Greek historian, the Ionian Hecataeus of Miletus. The works of Herodotus and Thucydides contain passages that appear to have been based on periploi.
Several examples of periploi have survived:
A periplus was also an ancient naval manoeuvre in which attacking triremes would outflank or encircle the defenders in order to attack them in the rear.