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The titles of the bematists’ geographies were all apparently Stathmoi (Stations), indicating that they organized their data according to the stopping points along an itinerary. This had its basis in the practical needs of travelers, who needed to know how to schedule their journeys and arrange where to stay overnight. This was made possible by the many stathmoi, quite literally “stops,” way-stations, and caravanserais which dotted the old routes of the Persian Empire, spaced approximately a day’s travel apart and serving as watering holes, camp-sites, and courier depots. The bematists took measurements using the stadion (or stade) and stathmos, though the parasang and schoinos were also employed when dealing with pre-existing Persian distances. The stade was a well-known unit, used throughout Greece, and the stathmos came into use in the Hellenistic period when long overland journeys became more common. Neither unit was a fixed or exact measurement but varied according to region of use and topography of the route being measured. A stade is typically estimated as around 184 meters, for purposes of rough conversions into modern measurement units (except for Egyptian stades, which were shorter, like the Egyptian schoinos). A stathmos not only denoted the stopping point on a route, but also the distance traveled between two stops, hence it measured one day’s travel, variable depending on how heavily laden the travelers and their pack animals were. Herodotus (5.53) reports 111 stations on the Persian royal road from Sardis to Susa, which measured 13,500 stades, and, reckoning that a day’s journey was 150 stades, he reports that the total travel time along the road was 90 days.

Herodotus (2.6, 5.53) describes the Persian parasang measure as 30 stades and the Egyptian schoinos as 60; by his account the Sardis to Susa route was 450 parasangs. Xenophon (Anab. 2.2.6, 5.5.4, 7.8.26) also gives 30 stades for the parasang, although the passages in the Anabasis with his journey calculations hint at the parasang as either a variable unit of measure or one employed more for narratological impact than mathematical accuracy (Rood 2010). Strabo (11.11.5) puts the parasang at 40 stades, noting that it varied between 30 and 60 stades according to different authorities, and he gives the same length and variations for the schoinos. Strabo credits Artemidorus (not Herodotus) with the schoinos equivalency of 30 stades, based on his distance from Alexandria to the vertex of the Nile delta (28 schoinoi, or 840 stades), although he notes that he himself saw measures of 40 stades and more used for schoinoi on the Nile, where a schoinos denoted the interval between each of the cities, which were not equidistant (17.1.24, 11.11.5). The anonymous late ninth-century Byzantine Sylloge Tacticorum, preserved in a single codex (Laur. 75.6), contains a short passage on distance units. It states that the Persian parasang had a variable measure, from Xenophon’s 30 stades to 60 for others, as reported by Strabo in a quote from Posidonius (Edelstein and Kidd 1989, F203). It is suggested that this author, instead of directly consulting Strabo, took this material from other secondary sources on either Strabo or Posidonius’s scientific writings (Kidd 1988: 729–730).

Roman explorers measured in miles (milia passuum), and Strabo (Strabo 7.7.4; fr. 56 (Jones)) reported that most people counted eight stades to the mile, although Polybius (Polyb. 34.12.4) added an extra two plethra, or one-third of a stade, making eight and one-third stades equal to one Roman mile. Walbank suggested that Polybius’s amendment was for greater accuracy over long distances and easier mathematical conversions from miles to stades (Walbank 1979, iii. 624): to convert m.p. to stades one simply multiplies the distance by 25 and divides by 3. The Sylloge Tacticorum author also comments upon conversions to miles in Strabo, mistaking Polybius’s eight and one-third stades to the mile as a proposal of eight and one-quarter by Eratosthenes, and he asserts that the mile was now conventionally reckoned as seven and one-half stades, a calculation also appearing in Aelian’s Tactica (Kidd 1988: 730). Censorinus (de die nat. 13.2), who wrote in the first half of the third century CE, went so far as to call the stade that was one-eighth of a mile (625 Roman feet) the “Italic stade” (Morgan 1973: 30). Roman authors generally used stades when handling material taken from the Greek geographers or when dealing with nautical distances, and except for a few exceptional uses of the stade, they employed miles for all land measurements taken by Roman surveyors (Morgan 1973: 34–35; Arnaud 1993: 242).