"a group of four" (tetra---, "four"), occurs in Acts 12:4 . A "quaternion" was a set of four men occupied in the work of a guard, two soldiers being chained to the prisoner and two keeping watch; alternatively one of the four watched while the other three slept. The night was divided into four watches of three hours each; there would be one "quaternion" for each watch by day and by night. Cp. the "guard" in Matthew 27:65; 28:11 .