« MIRIS MODIS REPENTE LIBER, FERREA ». — Hymn of the Vespers for the feast of St. Peter in Chains. It consists of a single stanza taken from the hymn *Felix per omne festum mundi cardines*, attributed to Elpidius, or rather to St. Paulinus of Aquileia.
The first two verses are a paraphrase of the account of the liberation of St. Peter (cf. Acts 12:6–11), recalled on this day when the dedication of the basilica of St. Peter in Chains is celebrated, built by Eudoxia on the Esquiline; the remaining three are inspired by Jesus’ command to Peter to feed his sheep and lambs (John 21:15–17).
BIBL.: C. Albini, *La poésie du Bréviaire*, Lyons n.d., pp. 318–319; G. C. Bell, *Gli inni dei Breviario tradotti*, Rome 1856, pp. 290–91; A. Mirra, *Gli inni del Breviario romano*, Naples 1947, p. 230.