Smith's Bible Dictionary
I. Jewish Army. - Every man above 20 years of age was a soldier, Numbers 1:3, each tribe formed a regiment, with its own banner and its own leader, Numbers 2:2; Numbers 10:14, their positions in the camp or on the march were accurately fixed, Numbers 2; the whole army started and stopped at a given signal, Numbers 10:5-6, thus they came up out of Egypt ready for the fight. Exodus 13:18. On the approach of an enemy, a conscription was made from the general body, under the direction of a muster-master, Deuteronomy 20:5; 2 Kings 25:19, by whom also the officers were appointed. Deuteronomy 20:9. The army had then divided into thousands and hundreds under their respective captains, Numbers 31:14, and still further into families. Numbers 2:34; 2 Chronicles 25:5; 2 Chronicles 26:12.
With the king, arose the custom of maintaining a body-guard, which formed the nucleus of a standing army, and David's band of 600, 1 Samuel 23:13; 1 Samuel 25:13, he retained after he became king, and added the Cherethites and Pelethites. 2 Samuel 15:18; 2 Samuel 20:7. David further organized a national militia, divided into twelve regiments under their respective officers, each of which was called out for one month in the year. 1 Chronicles 27:1. It does not appear that the system established by David was maintained by the kings of Judah; but in Israel the proximity of the hostile kingdom of Syria necessitated the maintenance of a standing army. The maintenance and equipment of the soldiers at the public expense dated from the establishment of a standing army. It is doubtful whether the soldier ever received pay even under the kings.
II. Roman Empire Army. - The Roman army was divided into legions, the number of which varied considerably (from 3000 to 6000), each under six tribuni ("chief captains"), Acts 21:31, who commanded by turns. The legion was subdivided into ten cohorts ("band"), Acts 10:1, the cohort into three maniples, and the maniple into two centuries, containing originally 100 men, as the name implies, but subsequently from 50 to 100 men, according to the strength of the legion.
There were thus 60 centuries in a legion, each under the command of a centurion. Acts 10:1; Acts 10:22; Matthew 8:5; Matthew 27:54. In addition to the legionary cohorts, independent cohorts of volunteers served under the Roman standards. One of these cohorts was named the Italian, Acts 10:1, as consisting of volunteers from Italy. The headquarters of the Roman forces in Judea were at Caesarea.
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Smith, William, Dr. Entry for 'Army'. Smith's Bible Dictionary. https://www.studylight.org/dictionaries/eng/sbd/a/army.html. 1901.