The Altemps Chapel, in the church of Santa Maria in Trastevere, was commissioned by Cardinal Marco Sittich von Altemps and built by Martino Longhi the Elder (1534-91). It was completed in 1587. As well as acting as a burial chapel for himself, the cardinal intended it as a commemoration of the Council of Trent (1545-63), which was formally closed by his uncle Pope Pius IV (r. 1559-65).
The coats-of-arms of Cardinal Altemps and of Pope Pius IV are displayed above the entrance, and their portraits feature in a niche high above the altar. The frescoes and the stucco work are the work of Pasquale Cati (c.1550-c.1620). The ornate vault features a fresco of the Assumption of the Virgin Mary in the central tondo, with the other panels depicting scenes from her life, interspersed with four smaller tondi depicting the four Evangelists.
The altarpiece takes the form of an ancient icon (6th-9th century), which is known as the Madonna della Clemenza. It may be one of the oldest icons of the Virgin Mary in existence.