E. Cobham Brewer 18101897. Dictionary of Phrase and Fable. 1898.
The Hebrews divided the night into four watches: 1, The beginning of the watches or even (Lam. ii. 19); 2, The middle watch or midnight (Judg. vii. 19); 3, The cock-crowing; 4, The morning watch or dawning (Exod. xiv. 24).
Ye know not when the master of the house cometh, at even, or at midnight, or at the cock-crowing, or in the morning.Mark xiii. 35.
The Romans divided the night into sixteen parts, each one hour and a - half, beginning at midnight. The third of these divisions (3 a.m.) they called gallicinium, the time when cocks begin to crow; the next was conticinium, when they ceased to crow; and fifth was diluculum, dawn.
Probably the Romans sounded the hour on a trumpet (bugle) three times, and if so it would explain the diversity of the Gospels: Before the cock crow (John xiii. 38, Luke xxii. 34, and Matt. xxvi. 34); but Before the cock crow twice (Mark xiv. 30)that is, before the bugle has finished sounding.
Apparitions vanish at cock crow. This is a Christian superstition, the cock being the watch-bird placed on church spires, and therefore sacred.
The morning cock crew loud,
And at the sound it [the Ghost] shrunk in haste away,