Castle

a military fortress (1 Chr. 11:7), also probably a kind of tower
used by the priests for making known anything discovered at a
distance (1 Chr. 6:54). Castles are also mentioned (Gen. 25:16)
as a kind of watch-tower, from which shepherds kept watch over
their flocks by night. The "castle" into which the chief captain
commanded Paul to be brought was the quarters of the Roman
soldiers in the fortress of Antonia (so called by Herod after
his patron Mark Antony), which was close to the north-west
corner of the temple (Acts 21:34), which it commanded.