The Angelus is a prayer traditionally said three times a day: morning, noon and evening in memorial of the incarnation of Christ in Mary's womb--a feast which we will celebrate on Monday, March 26th this year.
In the years before watches, churches would ring their bells to remind the faithful to stop and pray.
By the way, in spite of my Catholic upbringing and art history classes, for many years, I never knew that the famous painting above was in fact a Catholic subject. Entitled, The Angelus, by Jean Francois Millet it depicts French peasants stopping their work at the sound of the bell to pray the Angelus.
The Angelus
V. The Angel of the Lord declared unto Mary.
R. And she conceived of the Holy Spirit.
Hail Mary, etc.
V. Behold the handmaid of the Lord.
R. Be it done unto me according to thy word.
Hail Mary, etc.
V. And the Word was made Flesh.
R. And dwelt among us.
Hail Mary, etc.
V. Pray for us, O holy Mother of God.
R. That we may be made worthy of the promises of Christ.
LET US PRAY
Pour forth, we beseech Thee, O Lord, Thy grace into our hearts, that we to whom the Incarnation of Christ Thy Son was made known by the message of an angel, may by His Passion and Cross be brought to the glory of His Resurrection. Through the same Christ Our Lord. Amen.