Vigils is a term for night prayer in ancient Christianity. See Vespers, Compline, Nocturns, Matins, and Lauds for more information. A vigil is a night spent in prayer.
The practice of rising at about the middle of the night, for the purpose of prayer, is as old as the Church. The word "Vigils", at first applied to the night office, also comes from a Latin source, both as to the term and its use, namely the vigiliae or nocturnal watches or guards of the soldiers. The night from six o'clock in the evening to six o'clock in the morning was divided into four watches or vigils of three hours each, the first, the second, the third, and the fourth vigil. From the liturgical point of view and in its origin, the use of the term was very vague and elastic. Generally it designated the nightly meetings, synaxes, of the Christians. Under this form, the watch (vigil) might be said to date back as early as the beginning of Christianity. The liturgical service was composed of readings, singing of psalms, and various prayers, followed by the Eucharistic service.
During the 3rd century and 4th century, in addition to the celebration of Mass, it was customary to hold a vigil, which was a prayer service in three parts, on the night before a feast day. Vigils, in a strict sense, were night-watches in preparation for the feast. Commenced in the evening, they terminated only the following morning, and involved, in addition to the eucharistic supper, homilies, chants, and divers offices.
The Office of the Vigils was a single Office, recited without interruption at midnight. The number of psalms, which at first varied, was subsequently fixed at twelve, with the addition of a lesson from the Old Testament and another from the New Testament. From this vigil service developed three of the canonical hours: Vespers, Matins, and Lauds, inasmuch as the first was prayed the preceding evening, and the last was held in the early hours of the morning. This was the arrangement already in the days of Hippolytus (†236). St.Benedict of Nursia, in his description of the liturgy of the hours, always refers to vigils as the night office. After the vigil service had split into Vespers, Matins, and Lauds, Matins became three divisions known as nightwatches or nocturns.