Were today not Sunday it would, as it is October 14th, be the feast of Pope St Callistus I (d. 222). Callistus, also, and probably better known as Calixtus, was elected bishop of Rome in 217, succeeding Pope St. Zephyrinus. Our chief sources for him are the tendentious Philosophoumena or Refutatio omnium haeresium of an Hippolytus who tends be called Hippolytus of Rome and the not altogether reliable Liber pontificalis. According to Hippolytus, Callistus had been born into servile status and had twice been punished for crimes. In the second instance he had been sentenced to the mines in Sardinia and probably at that time ceased to be the property of his former master, a Christian of the Imperial household. Some nine or ten years after Callistus's release from the mines Pope Zephyrinus put him in charge of the Christian cemetery at Rome that still bears Callistus's name. There is an illustrated, Italian-language, page on the cemetery of Callistus here.
There is more about the stories of his earlier life and about his death in the online account which can be read here.
In his brief pontificate Callistus condemned Sabellius for heresy. Though he died under Alexander Severus, who is not known to have persecuted Christians, by the earlier fourth century Callistus. had come to be considered a martyr. The Depositio martyrum of the Chronographer of 354 enters under today Callistus's laying to rest at a milestone that accords with the location of the cemetery of Calepodius. The latter is given as the site of Callistus's burial by both the Liber pontificalis and Callistus's legendary Passio (BHL 1523; oldest witness is of the ninth century and a condensed version in hexameters is in the earlier to mid-tenth-century De triumphis Christi in Italia of Flodoard of Reims). Callistus's remains are said to have been translated, perhaps by Pope Gregory III (731-741), to Rome's church of Santa Maria in Trastevere where later Pope Gregory IV (827-844) gave him the honour of re-burial in the church's apse. Callistus. third from the left, is depicted in the late thirteenth-century apse mosaic (ca. 1290; attributed to Pietro Cavallini) in Santa Maria in Trastevere which can be viewed here.
In 854 relics believed to be those of St Callistus were translated by count St. Evrardus (Everardus) of Friuli to the monastery he had founded at today's Cysoing (Nord) in French Hainaut. The monastery, which survived until 1792, took Callistus's name but in 892 it became a dependency of the church of Reims and his relics, teste Flodoard in his Historia ecclesiae Remensis, were translated thither in the same year and laid to rest in the cathedral, next to those of St. Nicasius of Reims.
Since the early fifteenth century a head thought to be Callistus's has been in St. George's Chapel of Český Krumlov Castle. The website for the castle at Český Krumlov (in German: Böhmisch Krumau) in Bohemia is here.
St Callistus is portrayed in an earlier thirteenth-century statue on the trumeau of the central portal of the north transept of the present cathédrale Notre-Dame in Reims which, as mentioned above, housed some of his relics:
There is another view of the statue here:
Image: Wikimedia Commons
This statue is, I think, interesting not because it is portrait, which it clearly is not - although it does suggest a similar iconography to the mosaic in Santa Maria in Trastevere in the link above - but because it depicts a Pope as he was expected to appear when vested to an early thirteenth century audience - the tiara still has only one circlet, and the Pope appears to be wearing a rationale over his pallium.
Spurious letters of St Callistus are included in the collection known as the False Decretals. One of these decrees fasting in each of four seasons - the Ember Days. Here, in a earlier fourteenth-century (ca. 1326-1350) collection of French-language saint's lives, is an image of Callistus promulgating this decree, again wearing an early form of the Papal tiara:
Source: Paris, BnF, ms. Français 185, fol. 201r
St Callistus is shown at the left, baptizing, in a later fifteenth-century copy (1463) of Vincent of Beauvais' Speculum historiale in its French-language version by Jean de Vignay. In this picture he wears the familiar triple crown tiara:
Source: Paris, BnF ms. Français 51, fol. 9r
In England the one chapel dedicated to St Callistus that comes to my mind is in the south transept of Wells cathedral, which has a handsome modern stained glass depiction of him, wearing a triple tiara.
Adapted, with additional comments of my own, from John Dillon's post on the Medieval Religion discussion group.