Sometimes the Greeks needed to be quite certain when something happened. For example, here is a quote from a translation of “The History of the Peloponnesian War” by Thucydides, book 2, Chapter VI
“The thirty years' truce which was entered into after the conquest
of Euboea lasted fourteen years. In the fifteenth, in the forty-eighth
year of the priestess-ship of Chrysis at Argos, in the ephorate of
Aenesias at Sparta, in the last month but two of the archonship of
Pythodorus at Athens, and six months after the battle of Potidaea,
just at the beginning of spring, a Theban force a little over three
hundred strong, under the command of their Boeotarchs, Pythangelus,
son of Phyleides, and Diemporus, son of Onetorides, about the first
watch of the night, made an armed entry into Plataea, a town of Boeotia
in alliance with Athens.”