The Stadiasmus Maris Magni (Ancient Greek: Σταδιασμός ήτοι περίπλους της μεγάλης θαλάσσης) is an ancient Roman periplus or guidebook detailing the ports sailors encounter on the shores of the Mediterranean Sea.^[1] The stadiasmus provides distances, sailing directions and descriptions of specific ports.^[2] It was written in Ancient Greek and survives in fragments. The work was written by an anonymous author and is dated to the second half of the third century AD.^[3] The most complete Greek text together with a Latin translation was published in 1855 by Karl Müller as part of his work Geographi Graeci Minores.^[4]