By the early 9th century, Pliska was surrounded by a defensive wall and of land was further enclosed by an outer earthwork with stone revetment long. After the Byzantine army sacked and burned Pliska in 811, led by the emperor Nikephoros I (), Pliska was rebuilt by Omurtag (), who used "spolia" from nearby Roman buildings and employing late Roman-inspired rectilinear and basilica plans in the architecture of his new ashlar palace, which descended from Late Antique prototypes like Diocletian's Palace at Split, Croatia. When Boris I () converted to Christianity in 864, the religious buildings of Pliska were adapted for Christian use and it was after this point that the Great Basilica was constructed, together with a monastery which was attached to it. The monastery was home to the disciples of Saints Cyril and Methodius.