The Oracle of Delphi had started vacillating before its actual final abolition at the end of the 4th century A.D. Already in the course of the 3rd century the Mystery Cults of the East had prevailed in the subconscious of the pious flock, who asked for a revelatory truth rather than mere oracles. The anti-pagan legislation of Constantine the Great and his successors, particularly of Constantius, was a severe blow to the ancient sanctuaries. The removal of precious ex-votos and its remaining property deprived Delphi of the necessary funds for its existence. The pagan emperor Julian tried in vain to reverse the religious climate. The answer that his envoy, the famous doctor Oreibasios, received when he visited Delphi in order to ask for an oracle for the future of the pagan world, left no hope:

Εἴπατε τῷ βασιλεῖ, χαμαὶ πέσε δαίδαλος αὐλά,
οὐκέτι Φοῖβος ἔχει καλύβην, οὐ μάντιδα δάφνην,
οὐ παγὰν λαλέουσαν, ἀπέσβετο καὶ λάλον ὕδωρ.

[Tell the king that the flute has fallen on the ground. Phoebus doesn't have a home any more, nor an oracular laurel, nor a talking fountain, because the eloquent water has dried out]

This is considered to be the last prediction ever pronounced by the oracle. In 394 Theodosius I issued a decree which banned the oracles in the entire Roman Empire. However, the archaeological data from the Late Roman period, particularly the excavation reports of the 1990s, prove that life in Delphi did not stop in the 4th century. On the contrary, the city seems to have continued to exist and to offer its inhabitants high living standards for three more centuries. In the course of the Great Excavation there were discovered capitals, parapets and slabs from an early Christian basilica (5th century), when Delphi was a bishopric. Other important Late Roman buildings are the Eastern Baths, the peristyle house, the Roman Agora, the large cistern, the mansion in the western portico as well as the tombs outside the city, and the pottery kilns at the Gymnasium.
Among these monuments, the Southeastern Mansion, which has been excavated to the southeast of the precinct of the sanctuary of Apollo constitutes an important token of the prosperity and fine aesthetics of its inhabitants. It is a building with a 65-meters long façade, built on four different levels. It has private baths as well as four triclinia, of which three end up in niches. In its storage spaces large jars were discovered; in the rest of the rooms were found luxurious items and vessels. Among them stands out a small leopard made of mother-of-pearl, apparently of oriental provenance, possibly from Sassanian Persia; it was used as a decorative element for a small scepter or for a seatback. It seems that the building was used as a private house from the beginning of the 5th century until about 580 A.D. In about 590 it was transformed into an industrial centre where potters had settled. It is in this period that an abrupt change took place in the life of the city of Delphi, causing a demographical decline. The settlement shrank in size, the imports of luxurious items ceased and the local pottery production increased. Whereas the imported pottery items consist mainly of tableware, notably made of fine terra sigillata, the local products – amphoras, jugs, cooking pots etc – are coarser, made of red clay with addition of mica.
It is interesting to follow the changes of use of the area after the oracle and the sanctuary ceased functioning. The Sacred Way remained the main street of the settlement and was in fact paved anew using ancient building material. However, its character had now become primarily industrial and commercial. In the Roman Agora important workshops were excavated with pottery finds dating to the 4th century, of which one was perhaps used for making glass. Scattered architectural members indicate that maybe on that spot was built the only intra muros early Christian basilica. The western part of the site was the residential area, with large houses, many of which were provided with triclinia. Two large cisterns supplied water to the city as well as to the large bath complex built against the support wall of the sanctuary. As mentioned before, the city of Delphi was abandoned after the first decades of the 7th century, probably around 620 A.D. or slightly later.