The Church of the Holy Apostles stands at an important crossroads in the southeast corner of the area of the ancient Agora. The earliest church on the site, built over a wall of the 5th-century B.C. Mint and the foundations of the Roman Nymphaeum, is here dated to the last quarter of the 10th century on the basis of its plan and details. The original plan was revealed as a tetraconch cross-in-square with dome on pendentives carried on arches supported by four freestanding columns, the west of the four apses penetrating into the narthex. Fifteen tombs of this first period were excavated under the floor of the church proper and the narthex. In a second period, probably in the late 17th or early 18th century, repairs after damage from the 1687 fighting made changes in the narthex and dome and the interior was covered with paintings. War in 1826 again caused damage which was repaired in Period III with further changes and additions. Finally in 1876-1882 (Period IV) the west end was again rebuilt and the last vestiges of the west apse removed. The architectural type is studied in relation to other churches in Greece, and the restoration is described. The plates give the author's photos of the structure before, during, and after restoration and drawings of elevations, sections, and plans.