Baruch Adonai L'Olam (Maariv)
Baruch Adonai L'Olam is a prayer that is recited during Maariv in the Ashkenazi tradition on weekdays immediately preceding the Amidah. It contains 18 verses followed by a blessing titled Yiru Eineinu (may our eyes see).
The prayer was composed during talmudic times when synagogues could not be built in residential areas, and when Maariv was held in open fields. Its 18 verses took the place of the 18 blessings of the Amidah. The Amidah would then be recited in full privately by participants when they returned to their homes.