Psalms are the texts included in the biblical Book of Psalms and retaining an important place in the services of the Catholic Divine Office, sung to plainchant. The biblical texts are not metrical and therefore use a relatively simple form of chant that can be expanded by the use of a longer reciting note, the final syllables sung to a short syllabic formula. After the Reformation of the early 16th century metrical versions of the Psalms became current, with texts that could be sung to hymn-tunes. Harmonized settings of the biblical and metrical Psalms have been current in Protestant churches and chapels since the 16th century.