The Collaborative International Dictionary
Plethron \Pleth"ron\, Plethrum \Pleth"rum\, n.; pl. Plethra. [NL., fr. Gr. ?.] (Gr. Antiq.) A long measure of 100 Greek, or 101 English, feet; also, a square measure of 10,000 Greek feet.
n. A Greek unit of cord measurement, equivalent to one hundred podes.
Plethron is a measurement used in Ancient times, equal to 100 Greek feet (ποῦς, pous). It was roughly the width of a typical athletic running-track, and was used as the standard width and length of a Wrestling square, since wrestling competitions were held on the racing track in early times.
A plethron is given as the size of the wrestling area by Libanius in Orationes Chapter 10.
Although the standard measure for a plethron may have varied from polis to polis, it normally corresponded to the length of around 30 meters (100 ft). A square plethron is consequently a square of around 30 by 30 meters, i. e. something like 900 square meters.
The plethron continued to be used in the Byzantine Empire and was defined as 100 feet or 40 paces (bema/βῆμα).
The plethron was also used as a measure of area (i.e., as a square plethron). This functioned as the Greek acre and varied in size to accommodate the amount of land a team of oxen could plow in a day. Under the Byzantine Empire, these differences were codified among different themes and the unit came to be known as the " stremma", which continues as a (now metric) unit in modern Greece.