The Byzantine Empire until the 12th Century

After the division of the Roman Empire in AD 395, Lemnos passed to the Eastern Roman (Byzantine) Empire, continuing to enjoy a period of peace and stability. It had a shipyard in which the ships of the Byzantine fleet were built and repaired, particularly during the period of zenith for the Byzantine Navy – that is, from the ninth to the twelfth century. 

The period of security and stability was shaken in AD 900, when the Aegean islands became the prey of the marauding raids of pirates and especially of the Saracens, who had captured Lemnos. In 923-924, the Byzantine admiral Ioannes Rhadinos exterminated the pirates, defeating in a sea battle fought close to the island the infamous pirate Leo of Tripoli, and ridding it and the other islands of the scourge of piracy. 

During the period when Byzantium was mistress of the seas and the Byzantine fleet was supreme in the Aegean, there was intense activity in building forts in strategic positions. It was a common phenomenon at that time for the forts to be built on top of ancient acropolises and the remains of the buildings on these citadels to be incorporated as spolia in the new construction. The Byzantines continued in the main to apply the same mode of fortification as in antiquity, with minor modifications and improvements, because essentially there was no significant change in the weaponry, at least until the first half of the fourteenth century. The forts were usually formed by high, vertical fortification walls and tall towers with battlements, loopholes and machicoliations. 

In 1183-1185, the geographically nodal and strategically critical location of Lemnos led Emperor Andronikos I Komnenos to build a small but strong fortress upon the acropolis of Myrina (it is believed that a previous fort of the early 12th century was strengthened). Architectural members from the ancient acropolis, as well as stones from the in-situ quarrying of the rocks were used in its construction. 

The exact size and form of the castle built by Emperor Andronikos I Komnenos is not known. However, the acropolis was still the north boundary of the city, as in Classical times. In constructing the fortress upon the ancient acropolis of Myrina, the Byzantines did not alter the line of its fortification walls but continued to use them, while undoubtedly making many repairs and adaptations. 

Unfortunately, there is little information about the fortifications of this period in the castle of Myrina. It is very likely that future excavation on the kastro site will uncover important evidence of activities in these years. 

In 1204, the Crusaders of the Fourth Crusade captured Constantinople and founded an empire. In the sharing out of the territories of the Byzantine Empire by the victors, several islands in the Aegean were ceded to the Venetians, because they had served the Crusaders with their ships. The Venetians quickly spread in the Aegean islands, and in 1207 they established their dominion on Lemnos, making the castle of Myrina their administrative centre.