Lauda Sion Salvatorem is a sequence prescribed for the Roman Catholic Mass of Corpus Christi. It was written by St. Thomas Aquinas around 1264, at the request of Pope Urban IV for the new Mass of this Feast, along with Pange lingua, Sacris solemniis, Adoro te devote, and Verbum supernum prodiens, which are used in the Divine Office. The hymn tells of the institution of the Eucharist and clearly expresses the Catholic belief in transubstantiation. As with St. Thomas’ other three Eucharistic hymns, the last few stanzas are often used alone, in this case, the Ecce panis Angelorum.
Lauda Sion is one of only five medieval Sequences which were preserved in the Missale Romanum published in 1570 following the Council of Trent (1545–63). Before Trent many feasts had their own sequences. It is still sung today, though its use is optional in the post-Vatican II Ordinary form. The Gregorian melody is borrowed from the 11c sequence Laetabundi iubilemus attributed to Adam de Saint-Victor.
All of the above is taken from WikiPedia. Now for YouTube…
The chant version (as St. Thomas wrote it), sung by the Benedictine Monks of the Abbey of St. Maurice & St. Maur:
A polyphoic setting by Tomás Luis de Victoria, performed by an unidentified ensemble:
Another polyphonic setting, this one by Pierluigi da Palestrina, performed by Musica Humana Ada: