Semaxii

Semaxii a name mentioned by Tertullian as sometimes applied to Christian martyrs by their persecutors, from the fact that those who were burned alive were usually tied to a board or stake of about six feet in length, which the Romans called semaxis. — Bingham, Christ. Antiq. bk. 1, ch. 2, § 10.

⇒See also the International Standard Bible Encyclopedia.