The church of Santa Maria in Cosmedin was founded by Pope Adrian I (r. 772-95). The church 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.
Cosmedin comes from the Greek word kosmidion, which means ornamental, and refers to the splendid decoration of the 8th century church. The English word cosmetic has the same origin.
The enclosed choir (schola cantorum) and the beautiful cosmatesque pavement survive from the early 12th century.
In the second chapel on the left is a reliquary, which contains the purported skull of St Valentine.
The church preserves in its portico a much-photographed Ancient Roman drain-cover, known as the Mouth of Truth (Bocca della Verita).