A forerunner of the guidebook was the "periplus", an itinerary from landmark to landmark of the ports along a coast. A "periplus" such as the "Periplus of the Erythraean Sea" 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. This work was possibly written in the middle of the 1st century CE. It served the same purpose as the later Roman itinerarium of road stops.