Santa Maria in Cosmedin was founded by Pope Adrian I (r. 772-95). Cosmedin comes from the Greek word kosmidion (a thing of beauty).
The church, which boasts an eclectic collection of ancient Roman columns, stands on the site of an imperial-era building, perhaps the Statio Annonae It was substantially restored in the early-12th century and 600 years later it was given a Baroque makeover, including a new facade, by the architect Giuseppe Sardi (1680-1768). The Baroque additions were removed at the end of the 19th century.
The marble door case of the main door is well worth inspecting. Dating back to the 11th century, it is the work of Giovanni di Venetia. It has charming details, including little birds, foliage, a hand raised in blessing, the symbols of the Evangelists and the inscription: ME FECIT IOHANNES DE VENETIA.
The enclosed choir (schola cantorum) and the beautiful Cosmatesque pavement survive from the restoration work of the early-12th century, which was carried out by Cardinal Alfano. The schola cantorum, in particular, is a precious mediaeval survival, being an enclosure for the singers of the liturgy; there is another at the church of San Clemente. The floor level is one step higher than the nave and the Cosmatesque pavement is of greater intricacy.
The late-13th century baldacchino over the high altar (an ancient Roman bath) is signed DEODATUS ME FECIT (Deodatus made me).
In the second chapel on the left is a reliquary, which contains the purported skull of St Valentine.
The former sacristy, now the souvenir shop, is home to a fragment of an 8th century mosaic, which was executed under Pope John VII (r. 706-707) for a chapel in the old St Peter's. It is part of an image of the Adoration of the Magi. Santa Maria in Cosmedin preserves in its portico a hugely popular and much-photographed ancient Roman drain-cover, known as the Mouth of Truth (Bocca della Verita).
The Romanesque bell tower (ca. 1123), one of the finest in Rome, soars to a height of 34 metres (112 feet).