The Hebrew word ashmorah (אַשְׁמוּרָה) refers to a watch of the night, a division of time during nighttime hours. In ancient Israel and surrounding cultures, the night was divided into watches for guard duty. The Old Testament system used three night watches (Lamentations 2:19 — beginning of watches; Judges 7:19 — middle watch; Exodus 14:24 — morning watch), while the Romans used four watches (as referenced in the Gospels).
The night watch is a rich biblical metaphor for vigilant waiting on God. Psalm 63:6 describes meditating on God "through the watches of the night." Psalm 77:4 speaks of spiritual distress keeping one awake. Psalm 130:6 uses the image of watchmen longing for morning as a picture of the soul's longing for God: "My soul waits for the Lord more than watchmen wait for the morning." The concept of spiritual watchfulness — staying alert through spiritual "night" — runs through both Testaments and is central to Christian discipleship.