Early Byzantine Period (4th - 7th century A.D.)
When Great Constantine became king and moved the capital of the state to Constantinople establishing Christianity as the official religion, Thessaly was still a separate province, as it used to be, belonging administratively to the Eastern Illyrian and ecclesiastically to the pope of Rome.
The most significant cities of antiquity in the prefecture of Larissa, such as Larissa and Farsalos, continue to prosper, while a series of ancient urban centres are still mentioned in the sources until the end of the period,
From the end of the 4th c. a series of barbaric raids start, that caused the desolation of the countryside and tested the endurance of the fortified positions, many of which are ruined. Around the late 6th c A.D. Ioustinianos makes a great effort to restore many fortresses and to revitalise the cities, while he also establishes a new fortified city at the foot of Kissavos, which hasn't been identified to date.
The most significant new element of the period is the spreading of Christianity, which starts fairly early in Thessaly.
According to various sources, Saint Achillios, who was probably the first bishop of Larissa and who participated in the 1st Ecumenical Council, the sponsor of numerous charitable institutions in the city, who also oversaw the building of his own grave on the hill of the fortress, played a large part in spreading Christianity in Larissa.
In recent years, a significant early Byzantine basilica of the 6th c. A.D. built on two arch-covered illustrated burial chambers of noble personages, was excavated in this area. One of those could be associated to Saint Achillios, according to the inscriptions found at the site and to the references in his biography. Another important factor for the association, was the continued reverence for the saint in that area during the following eras, up to our days, by the successive relocations of the church, which has always been the metropolitan church of the city.
During recent excavations east of the church of Saint Achillios, a number of early byzantine and main byzantine buildings were revealed, indicating that this was the densely structured city centre. Amongst them, there is one more basilica and a bath.
Yet another large early byzantine basilica with notable mosaics and sculptured adornments has been excavated at the commercial centre of the city, while numerous other findings of the period, many of which were revealed in social buildings, prove that Larissa was a prosperous city in the early byzantine period, as well as an important artistic centre.
From an ecclesiastical viewpoint, the diocese of Larissa was promoted to a metropolis from very early on, over all the dioceses of Thessaly, which in those days reached Ypati in the South and Kessaria and Dioklitianoupoli in the North, today's W Makedonia. Of the present day, Prefecture of Larissa, mention is made of the dioceses of Farsalos - which became an archdiocese - and Thessalikon Salton (the latter is placed near the mouth of the Pinios).
References in Greek language:
Σδρόλια Στ., Δρ Βυζαντινής Αρχαιολογίας - Αρχαιολόγος 7ης ΕΒΑ.
ΤΕΔΚ Νομού Λάρισας, Οδηγός Νομού Λάρισας, Λάρισα 1998