TRISAGION. - From the Greek τρεῖς - ἅγιος: a hymn in which the word Sanctus is repeated three times. A distinction is made between the so-called biblical form and the non-biblical form of liturgical origin.
1) The biblical T., or the threefold Sanctus at the end of the Preface, is derived from Is. 6, 3 (cf. Apoc. 4, 8), and is therefore also called the "seraphic hymn". Already in use in the synagogue (cf. the "Keduscha" of the morning Office), it is found in Clement of Rome (ad Corint., chap. 34), in the liturgy of the Apostolic Constitutions, and in all Eastern liturgies beginning with the Euchologion of Serapion, from where it passed into Spain and Gaul (St. Hilary). It is not found in St. Justin or in the Traditio Apostolica of Hippolytus of Rome. It entered the Roman liturgy perhaps under Sixtus III (d. 440) from the Syrian liturgy. The liturgical form differs from the biblical one by adding the words Deus and caeli, while keeping the Hebrew word sabaoth. It was originally sung jointly by the priest and the people, later in the Carolingian period by the subdeacons, and now by the choir. It also recurs in the Te Deum (v.).
2) The T. of liturgical origin, an acclamation or hymn in honor of the Most Holy Trinity, occurs in the Byzantine rite in all the Offices; in the other Eastern rites it is used many times. In the Roman liturgy it is used in the preces at Prime, in the Rituale (ed. 1952, tit. X, 12) for the procession in quacunque tribulatione; it is found in the invocations engraved on bells. It derives, especially with the Improperia (v.) of Good Friday, between the 9th and 10th centuries, from the Gallican liturgy as a dramatic element of the act of adoration of the Holy Cross; it is sung in Greek with the Latin translation. A simple form and a paraphrastic form are distinguished, with various additions, e.g., «qui crucifixus es pro nobis», «qui venisti ab excelsis pati pro nobis» (Bobbio Missal, 25: dicitur post dios), «[Agnē Dei] qui tollis peccata mundi [miserere nobis]» or similar to Apoc. 4, 10-11, etc.