The periods into which the time between sunset and sunrise was divided. They are so called because watchmen relieved each other at each of these periods. There are frequent references in Scripture to the duties of watchmen who were appointed to give notice of the approach of an enemy (2 Samuel 18:24-27; 2Kings 9:17-20; Isaiah 21:5-9). They were sometimes placed for this purpose on watch-towers (2 Kings 17:9; 18:8). Ministers or teachers are also spoken of under this title (Jeremiah 6:17; Ezek. 33:2-9; Hebrews 13:17).
The watches of the night were originally three in number, (1) "the beginning of the watches" (Lamentations 2:19); (2) "the middle watch" (Judges 7:19); and (3) "the morning watch" (Exodus 14:24; 1 Samuel 11:11), which extended from two o'clock to sunrise. But in the New Testament we read of four watches, a division probably introduced by the Romans (Matthew 14:25; Mark 6:48; Luke 12:38). (See DAY .)
These dictionary topics are from M.G. Easton M.A., D.D., Illustrated Bible Dictionary, Third Edition, published by Thomas Nelson, 1897. Public Domain, copy freely.
Easton, Matthew George. "Entry for 'Watches'". "Easton's Bible Dictionary".