The sculptural details used for architectural decoration were movable material supplied for the new constructions, primarily extracted from the abandoned ruins of Roman and early Byzantine buildings. During the construction of the fortified khan's residence in Pliska, the extraction of ready-made construction material from nearby and distant abandoned ruins was widely used. Remains of brick walls were further demolished to remove and use the preserved solid bricks. The preserved whole architectural details like column capitals, marble slabs, stone bases and others which were located in the remains of the ancient settlements, were brought to the khan's residences.

Another way to supply architectural elements was military campaigns. Bulgarian rulers often took various sculptures and architectural elements from the conquered cities as military trophies during their campaigns. Such are, for example, the numerous columns with the carved names of fortresses in Eastern Thrace (the Byzantine theme of Macedonia), found in the palace in Pliska, which are associated mainly with Khan Krum and his victories.

Apart from the elements of the monumental sculpture found and taken as trophies, a large part of the sculptural compositions were built on site in the Bulgarian palaces themselves. The builders, artisans, artists, decorators and sculptors, who were brought to the Bulgarian lands as captives or hired to do certain tasks, led to the development of monumental sculpture. The use of foreign craftsmen led to the gradual adoption of Byzantine customs and practices in construction. The decoration of homes and halls intensified as a sign of prestige and personal dignity.

The Proto-Bulgarians knew well the monumental sculpture. But unlike all other steppe peoples (Khazars, Avars), the Proto-Bulgarians had a special practice that left remarkable monuments, unique in nature. They bear the specific name "devtashlari" and are known in Bulgaria only on the site of Pliska. These are groups of irregular stone blocks, rarely exceeding 2 m in height, driven 50-60 cm into the ground. Between the irregular stone blocks here and there are pieces of columns. Devtashlars are either incorrectly arranged or arranged in regular rows so as to form large rectangles or squares, usually oriented with the rotation of the planet.

Studies of these monuments and partial excavations around them, in which human and animal bones were found, as well as rare objects such as knives, arrowheads and horseshoes, show that the devtashlars were used to perform various rituals. It appears likely that they were associated with various sacrifices, which aimed to beg the mercy of the supreme god of the tribe.

The Devtashlars are also associated with the massive medieval aristocratic practice and phenomenon of erecting inscriptions on behalf of the khan for fallen generals who perished far from their homeland. The monumental sculpture and constructions in Danubian Bulgaria categorically show that the settlers of Asparukh did not come here as wild barbarians, but as bearers of a rich culture. They had a building tradition, mostly related to the construction of fortifications and protected settlements. Subsequently, borrowing various sculptural elements and styles used by the closest neighbour and natural rival Byzantium, the Proto-Bulgarians enjoyed and perfected their monumental sculptural art.