John Dillon posted the following piece on the Medieval Religion discussion group about the feast on August 1st of St. Peter ad Vincula.
This seems to have originated as the dedication feast of the Roman church of San Pietro in Vincoli, founded in the first half of the fifth century to house chains with which St. Peter was believed to have been been secured when he was imprisoned by Herod in Jerusalem (Acts 12: 5-11). At first called the titulus Eudoxiae (perhaps after Eudoxia, the wife of Emperor Valentinian III, thought by some to have helped pay for it), it was dedicated by Pope Sixtus III both to Peter and to Paul and for centuries was also known as the titulus Apostolorum. Its present designation (also late antique in origin) when expressed in Latin usually occurs as (Ecclesia) Sancti Petri ad vincula; hence also the customary Latin name of the feast,Sancti Petri ad vincula. The poet Arator gave a public reading of his De actibus Apostolorum in this church on four consecutive days in 544.
The church was restored by Pope Adrian I (772-95) and rebuilt under Pope Sixtus IV (1471-84) and again under Pope Julius II (1503-13). At some point chains thought to have held Peter when he was imprisoned at Rome prior to his execution were brought from the so-called Mamertine Prison (not attested as an ancient designation) and were added to those said to be from Jerusalem. According to legend, these fused of their own accord. They are now on display in the confessio and there are photographs here:
The legendary fusion of the two chains is paralleled hagiographically by legendary understandings that Peter, having been imprisoned at Rome prior to his execution there under Nero, was also released from that imprisonment by an angel and that he then started to flee the city only to be persuaded to return when chided by Christ in a vision (the "Quo vadis?" episode). Scenes of Peter's delivery from prison by an angel that occur in cycles portraying episodes from his apostolate are sometimes placed in such a way as to evoke both liberations, though in other instances their occurrence after an interaction with Nero or before the "Quo vadis?" encounter make it evident that the liberation portrayed is the one in Rome.
By the later Middle Ages St. Peter in Chains had become today's principal feast in the Roman church. In modern Roman Catholicism it was removed from the general Roman Calendar in 1960 but is still permitted at churches so titled.[ Also by groups such as FSSP - Clever Boy]
Further pertinent images from the period within the purview of this list (i.e. ending in the middle of the sixteenth century):
a) Peter's delivery from prison by an angel as depicted in a late tenth- or early eleventh-century troper from Autun (Paris, BnF, ms. Arsenal 1169, fol. 44v):
b) Peter's delivery from prison by an angel as portrayed in an earlier twelfth-century nave capital in the basilique cathédrale Saint-Lazare at Autun:
c) Peter's delivery from prison by an angel as depicted in the mid-twelfth-century mosaics of the Cappella Palatina in Palermo:
d) Peter's delivery from prison by an angel as depicted in a panel of the thirteenth-century Life of St. Peter window (choir, bay 10; some nineteenth-century restoration) in the cathédrale Saint-Pierre-et-Saint-Paul in Troyes:
Note the presence of cords rather than of the more usual chains. Vincula are simply "restraints used to bind someone or something" and thus are not necessarily of metal.
e) Peter's delivery from prison by an angel as depicted in a thirteenth-century missal for the Use of Arras (Arras, Bibliothèque municipale, ms. 0888 (0444), fol. 237v):
f) Peter's delivery from prison as depicted in a mid-thirteenth-century gradual for the Use of the abbey of Fontevrault (Limoges, Bibliothèque municipale, ms. 2, fol. 157r):
g) Peter's delivery from prison by an angel as depicted in a late thirteenth-century copy of French origin of the Legenda aurea (San Marino, CA, Huntington Library, ms. HM 3027, fol. 88v; view greatly expandable):
h) Peter's delivery from prison by an angel as depicted in a fourteenth-century copy of Guiard des Moulins' Bible historiale (Paris, BnF, ms. Français 152, fol. 457v):
i) Peter's delivery from prison by an angel as depicted in an earlier fourteenth-century antiphoner (betw. 1300 and 1350) of French origin (Rouen, Bibliothèque municipale, ms. 250, fol. 182r):
j) Peter in prison as depicted in a later fourteenth-century Roman missal (ca. 1370) of north Italian origin (Avignon, Bibliothèque-Mediathèque Municipale Ceccano, ms. 138, fol. 252v):
k) Peter's delivery from prison by an angel (lower register) as depicted Cenni di Francesco di Ser Cenni in a later fourteenth-century antiphoner (ca. 1380) in the Walters Art Museum in Baltimore (ms. W.153, fol. 35v):
l) Peter's delivery from prison by an angel as portrayed in relief on the late fourteenth- to early fifteenth-century west front (betw. 1385 and 1415) of the Dom St. Petri in Regensburg:
m) Peter's delivery from prison by an angel as depicted by Giacomo Jaquerio in an early fifteenth-century panel painting (betw. 1410 and 1415) in the Palazzo Madama, Turin:
n) Peter's delivery from prison by an angel as depicted by LLuis Borrassà (in Spanish, Luis Borrassá) in a panel, now displayed in the rectory of the esglésies de Sant Pere in Terrassa, Catalunya, from his dismembered early fifteenth-century altarpiece of Saint Peter (betw. 1411 and 1413) for that church:
o) Peter's delivery from prison by an angel as depicted in an earlier fifteenth-century breviary (ca. 1414) for the Use of Paris (Châteauroux, Bibliothèque municipale, ms. 2, fol. 259r):
p) Peter in chains as depicted as depicted in an earlier fifteenth-century Franciscan breviary (ca. 1430; Chambéry, Bibliothèque municipale, ms. 4, fol. 550r):
q) Peter's delivery from prison by an angel as portrayed by Luca della Robbia in an earlier fifteenth-century marble relief (1438 or 1439) in the Museo nazionale del Bargello, Florence:
r) Peter's delivery from prison by an angel as depicted by Konrad Witz in a panel from a dismembered mid-fifteenth-century altarpiece (1444) in the Musée d'Art et d'Histoire in Geneva:
s) Peter's delivery from prison by an angel as depicted in a later fifteenth-century tapestry of Flemish origin (Tournai, by 1464) in the Musée national du Moyen Age (Musée de Cluny), Paris:
t) Peter enthroned and, together with a kneeling angel, holding a broken chain (at left, cardinal Nicholas of Kues and an angel) as portrayed in relief by Andrea Bregno on the cardinal's later fifteenth-century tomb (1465) in Rome's basilica di San Pietro in Vincoli:
u) Peter's delivery from prison by an angel as depicted by Filippino Lippi in a late fourteenth-century fresco (1481-1482) in the Cappella Brancacci, chiesa di Santa Maria del Carmine, Florence:
Before restoration in the late twentieth century:
v) Peter's delivery from prison by an angel as depicted by Jesús María Parado del Olmo in a panel of his earlier sixteenth-century great altar (betw. 1500 and 1525) in the iglesia di San Pedro at Montealegro de Campos (Valladolid):
w) Peter's delivery from prison by an angel as depicted by Raffaello Sanzio in an early sixteenth-century fresco (ca. 1512-1514) in the Vatican palace's stanza di Eliodoro:
Detail view (Peter in chains):
x) Peter's delivery from prison by an angel as depicted in a panel of the mid-sixteenth-century Passion of Christ and Passion of St. Peter window (1540; restorations in 1880, 1964, and 1989-1990) in the église Saint-Pierre de Beignon (Morbihan):