The Monastery of Daphni lies at the foot of Mount Aigaleo, on a strategic spot along the ancient Sacred Way from Athens to Eleusis. According to Pausanias, in the same area there was a temple dedicated to Apollo ?Daphnaios? or ?Daphnephoros?.

The monastery was protected by defensive walls, 9m height, with towers, battlements and two entrance gates at the eastern and western part. Each side of the square fortification wall is app. 98 m long and 1 m thick. Today, only the northern part maintains the basic characteristics of the original layout: three protruding square towers and an inner blind arcade with a continuous ambulatory (pathway) running along the walls and the battlements on the top. The wall was originally reinforced by two more nowadays ruined towers, one at the western gate and one inner tower at the eastern gate.

Along the inner west, north and east walls lie the foundations of buildings which probably belong to the byzantine cells of the monastic complex.

In the center of the precinct stands the Catholicon (the main church of the monastery). Cells with porticos were built at the south side of the church, forming an almost square churchyard. The Catholicon dates back to the 11th c. and belongs to the octagonal cross-in-square type of church with dome, adopted by some very important monuments of the middle-byzantine period, such as the Catholicon of the Monastery of Ηοsios Loukas in Boeotia and that of the Nea Moni in Chios.

The exceptional quality of the building, with ancient architectural parts embedded in its masonry, the brick ornamentation around the windows and the luxurious interior with the unique wall mosaics of the 11th c. and the marble decoration, very few fragments of which are preserved, connect the foundation of the monument with circles of the imperial court of Constantinople. After the destruction of the marble revetments, the lower parts of the nave were decorated with frescoes, dating probably back to the 17th c., nowadays partly preserved.

The narthex on the west side of the church was built concurrently with the Catholicon, whereas a short while later a two-storey exonarthex (portico) was added. During the Frankish occupation of Attica (13th ? 14th c.), after a major earthquake that caused severe damages, the Cistercian monks (a Roman Catholic monastic order), to which the monastery was conceded by the Duke of Athens, Othon de la Roche, implemented extended restoration works in the exonarthex, giving it its present form, with the pointed arches on the facade and the crenelations on the upper floor.

Beneath the narthex of the Catholicon there is a barrel-vaulted crypt of unknown original use. The crypt was considered as the entombment site of the Dukes of Athens, due to a document of the Latin abbot of the monastery Frere Jacques mentioning the burial of the Duke Guy II de la Roche in the tomb of his «ancestors» in Daphni, in 1308. This theory is supported by the existence of marble sarcophagi in the cloister. However, the cemetery church of the monastery was the byzantine church of Agios Nikolaos, nowadays partly ruined, situated in a short distance to the SE of the monastic complex.

After the conquest of Athens by the Ottoman Turks in 1458, the monastery was given back to the orthodox monks, who constructed ? probably in 16th c. ? two-storey buildings containing cells, a refectory, storage rooms and a gallery around the small churchyard replacing the byzantine cells. These are the buildings restored and preserved nowadays.

The remnants of other auxiliary constructions of the byzantine period (cistern, bathhouse, probably a library) are found to the south and west of the yard. Τhe cistern, an underground, two-aisled, barrel-vaulted reservoir for the collection of rain water, is located behind the western wing of the post-byzantine cells. Its dimensions are 14 X 6 m and it is 7 m deep. The water was drawn from two spouts at either end of the cistern. An underground tunnel connects the cistern with the three wells supplying the monastery with water: one in the southern churchyard, one inside the ground floor hall of the eastern wing, known as «post-byzantine Refectory», and one outside of the monastery?s eastern gate. According to the tradition, it was through the underground tunnel that the Ottomans managed to gain access as a result of treachery and seized the monastery, where a group of Greek fighters had been barricaded during the revolution of 1821.

To the south of the cistern lie the ruins of the byzantine bathhouse, which could also be used by laymen, in exchange for a symbolic fee. The bathhouse was heated through the floor and the walls, where hot air circulated through clay pipes.

To the north of the Catholicon there are found the ruins of the byzantine Refectory (the dining hall for the monks), a long building with a semicircular conch at the eastern end. It had a brick pavement, a large part of which is maintained up today, and it was barrel-vaulted, as indicated by the massive pillars along the sides of the edifice.

Finally, the architectural remnants to the west of the exonarthex of the Catholicon belong to a rectangular, single-naved building of the post-byzantine period. The apse at its northern end was the reason for the building to be formerly considered as a chapel and identified with an edifice dedicated by the guild of grocers in 1764. More recent theories, however, regard the building as a monastic Refectory.

During the Greek Revolution of 1821 the monastic complex was occasionally used as a garrison. After the founding of the New Hellenic State (1830), the monastery was deserted and finally abandoned, after having housed, for a short while, barracks for the Bavarian (1838-1839) and French (1854) troops and the Public Psychiatric Hospital (1883-1885).

The restoration works of the monastic complex and of the mosaics of the Catholicon began at the end of the 19th c. and have been continued, periodically, up today by the Ministry of Culture and intensified after the disastrous earthquake in 1999, financed by European Funding Programs and the Greek State.

Since 1990, the Monastery of Dafni is inscribed in the World Heritage List (WHL) of UNESCO, as a serial registration along with the Monastery of Ηοsios Loukas in Steiri of Boeotia and Nea Moni in Chios.