The relic of the head of St. John the Baptist has been venerated in San Silvestro in Capite since at least the end of the twelfth century, the year 1192 or 1194 being probably the earliest date at which the words ‘de Capo’ or ‘de Capite’ are found added to the church’s name. How it came to be here has not been recorded, nor can its previous history or provenance be, at present, ascertained.
Tradition holds that John was executed in the prison of the fortress of Machaerus, near the Dead Sea. It is said that Herodias, who prompted her daughter to ask King Herod Antipas for his head, afraid that if his body and his head were buried together he might come back to life, had the head hidden in Herod’s palace in Jerusalem, while John’s disciples removed the body to Sebaste in Samaria.
There are two differing accounts of how the head was found in Jerusalem and made its long journey to Constantinople, but it is known with certainty that it was being venerated as the principal treasure of the monastery church of Saint John Baptist of Stoudios within the walls of that city in 873. It is not known if the head was entire at this time, or whether it had been broken into different fragments.
The relic in San Silvestro is not a full head, but the top part of a skull, which has been set into a wax skull. There is another relic in the Cathedral of Amiens in northern France, which is only the front part of a head, from the forehead down to the upper jaw, excluding the teeth.
The relic now venerated in San Silvestro as the head of Saint John the Baptist has been for centuries the focus of much devotion and prayer. It located in the chapel of the ‘Pietà’, accessible through a doorway immediately to the left on entering the church from the courtyard, or directly from Via del Gambero which runs along the side of the church.
"The rarity in a Roman church of a piece of this kind, even if it has not reached us fully in its original form, constitutes in itself a very interesting fact, and testifies […] to the priceless value obviously attributed to the relic enclosed therein" (Ilaria Toesca).
The ornamental reliquary is composed of parts from different historical periods. The more ancient part is the central gold-coloured section, which sits on a silver base and is crowned by a golden spired section, both of the latter dating to 1888, when the relic was being kept in the Vatican. The silver base was made as a gift from the Chapter and Clergy of the Vatican Basilica, Rome January 1, 1888, for Pope Leo XIII in honour of his golden jubilee of priesthood (he was in fact ordained priest on the Feast of San Silvestro, December 31st, in 1837) and is inscribed with some of Leo’s own verses. The top section is in the form of a gothic spire containing a small statue of the Baptist, and was crafted by the goldsmith Pietro Quadroli from a design by the painter Ludovico Seitz, who was at the time head of the Vatican Pinacoteca (art gallery). This replaced the original top piece which had been stolen from San Silvestro during the sack of Rome in 1527, the nuns there fortunately having managed to hide the central and most precious part of the reliquary containing the relic itself.
The outer part of this older central section consists of a six-sided Gothic-style shrine, commissioned by Cardinal Angelo Acciaiuoli, Archbishop of Florence (the Baptist is the city’s patron saint) in the time of Pope Boniface IX (1389-1404). It may have been commissioned for the jubilee years of 1390 or 1400 to enrich the solemn procession on August 29th, the feast of the Beheading, in which the relic was carried, until 1411, every year. The feet of the shrine consist of a small lion at each corner of the hexagon, each of which supports a statuette of a saint within a tiny shrine against a background of dark blue enamel. The saints are, alternately, St. George killing the dragon and St. Christopher carrying the Child Jesus, with a small balustrade running between them forming the outer wall of this lower outer hexagonal section. Just above this is an inner hexagonal section, with a slender spire rising at each corner up the remaining height of this central section. Each of the six inner sides of this inner hexagon is adorned with a translucent enamel panel featuring scenes of the life of the Baptist: the first three panels each contain two scenes (“Gabriel announces John’s birth to Zechariah” and “John's Birth”; “The child John goes to the desert" and “John indicates Christ to his Disciples”; “The Baptism of Christ” and “John rebukes Herod”) while the last three each contain just one scene (“John's Beheading”, “Herod's Banquet”, “Herodias receives John’s head from her daughter”). The scene of the beheading naturally takes pride of place in the front centre and is depicted as already having been completed, in order to give maximum prominence to the detached head and the mounted soldiers waiting to receive it.
Just above these panels sits the part containing the relic itself. Above the latter, the slender spires are each joined to their neighbours by a consisting of a decorative pointed arch with an identical rosette on each side of it. The rosette contains a coat of arms surmounted by an episcopal mitre and a stylized flower. In every second arched panel, the rosettes contain the coat of arms and colours of Cardinal Acciaiuoli who commissioned the work (silver lion in blue field), while the alternate ones contain those of the Tomacelli family to which Pope Boniface IX belonged (red, with a chequered band of silver and blue) respectively. Above the arches and rosettes is another small balustrade, above which the slender pillars are each crowned by a small statue of a saint, possibly alternately St. Paul (with a sword) and St. Peter (perhaps with keys).
Inside the Acciaiuoli reliquary sits another older silver reliquary locked into the newer structure, with six sides. While the base, roof and frame of this reliquary are silver, the six walls were each originally made up of a rock crystal slab of which only three remain, which are of great purity and perfection.
The relic itself is a skull which is missing the jaw, remodelled and mostly filled with wax and stucco. The back of the skull is protected by a rigid silver half-cap which continues into a kind of silver “chin guard” under the bottom of the skull. This replaces the missing jaw and is secured by two lateral brackets to another rigid cap decorated with lilies, which covers the top of the skull. The outer ring of this is adorned with alternating red and dark blue precious stones, probably a variety of rubies and sapphires. This cap is joined to the rear half-cap by a hook and it has a ring attached to it, which allowed the relic to be easily extracted from the display case. Above this "half-cap " sits a real, golden crown, consisting of a series of 18 articulated plates, joined by hinges, and also decorated with lilies. The plates and the lilies are each decorated by a cabochon stone alternately red or green, and pearls.
In 1999, the reliquary was taken to the Central Institute for Restoration (Istituto Centrale per il Restauro), in Rome for restoration for about 13 years, returning to San Silvestro in June 2012. It is back in its normal place of display in the Pietà Chapel, but now in a special temperature-controlled enclosure in order to help better preserve the priceless relic.