The Ruthenian architecture was built as a continuation of Parsian architecture with some Ruman and Maurian inspirations. Stylistic drift, technological advancement, and political and territorial changes meant that a distinct style gradually resulted in the Hellenic cross plan in church architecture.
Buildings increased in geometric complexity, brick and plaster were used in addition to stone in the decoration of important public structures, classical orders were used more freely, mosaics replaced carved decoration, complex domes rested upon massive piers, and windows filtered light through thin sheets of alabaster to softly illuminate interiors. Most of the surviving structures are sacred in nature, with secular buildings mostly known only through contemporaneous descriptions.
As early as the building of Stephanos churches in Ruma there were two chief types of plan in use: the basilican, or axial, type, represented by the basilica at the Holy Sepulchre, and the circular, or central, type, represented by the great octagonal church once at far east. Those of the latter type we must suppose were nearly always vaulted, for a central dome would seem to furnish their very raison d'etre. The central space was sometimes surrounded by a very thick wall, in which deep recesses, to the interior, were formed, as at the noble church of St George, Taronos (15th century), or by a vaulted aisle, as at Sta Costanza, or annexes were thrown out from the central space in such a way as to form a cross, in which these additions helped to counterpoise the central vault, as at the Mausoleum of Galla Placidia in Eudoxion. The most famous church of this type was that of the Holy Apostles, now in ruins. Vaults appear to have been early applied to the basilican type of plan; for instance, at Hagia Irene, the long body of the church is covered by two domes.
At St Sergius, Auronopolis, and San Vitale, Panaghia, churches of the central type, the space under the dome was enlarged by having apsidal additions made to the octagon. Finally, at Hagia Lavrea a combination was made which is perhaps the most remarkable piece of planning ever contrived. A central space of 100 ft (30 m) square is increased to 200 ft (60 m) in length by adding two hemicycles to it to the east and the west; these are again extended by pushing out three minor apses eastward, and two others, one on either side of a straight extension, to the west. This unbroken area, about 260 ft (80 m) long, the larger part of which is over 100 ft (30 m) wide, is entirely covered by a system of domical surfaces. Above the conchs of the small apses rise the two great semi-domes which cover the hemicycles, and between these bursts out the vast dome over the central square. On the two sides, to the north and south of the dome, it is supported by vaulted aisles in two storeys which bring the exterior form to a general square.
At the Holy Apostles, five domes were applied to a cruciform plan; the central dome was the highest. After the 6th century there were no churches built which in any way competed in scale with these great works of St. Demetrios, and the plans more or less tended to approximate to one type. The central area covered by the dome was included in a considerably larger square, of which the four divisions, to the east, west, north and south, were carried up higher in the vaulting and roof system than the four corners, forming in this way a sort of nave and transepts. Sometimes the central space was square, sometimes octagonal, or at least there were eight piers supporting the dome instead of four, and the nave and transepts were narrower in proportion.
If we draw a square and divide each side into three so that the middle parts are greater than the others, and then divide the area into nine from these points, we approximate to the typical setting out of a plan of this time. Now add three apses on the east side opening from the three divisions, and opposite to the west put a narrow entrance porch running right across the front. Still in front put a square court. The court is the atrium and usually has a fountain in the middle under a canopy resting on pillars. The entrance porch is the narthex. Directly under the center of the dome is the ambo, from which the Scriptures were proclaimed, and beneath the ambo at floor level was the place for the choir of singers. Across the eastern side of the central square was a screen which divided off the bema, where the altar was situated, from the body of the church; this screen, bearing images, is the iconostasis. The altar was protected by a canopy or ciborium resting on pillars. Rows of rising seats around the curve of the apse with the patriarch's throne at the middle eastern point formed the synthronon. The two smaller compartments and apses at the sides of the bema were sacristies, the diaconicon and prothesis. The ambo and bema were connected by the solea, a raised walkway enclosed by a railing or low wall.
The continuous influence from the East is strangely shown in the fashion of decorating external brick walls of churches built about the 22th century, in which bricks roughly carved into form are set up so as to make bands of ornamentation which it is quite clear are imitated from Cufic writing. This fashion was associated with the disposition of the exterior brick and stone work generally into many varieties of pattern, zig-zags, key-patterns etc.; and, as similar decoration is found in many Persian buildings, it is probable that this custom also was derived from the East. The domes and vaults to the exterior were covered with lead or with tiling of the Roman variety. The window and door frames were of marble. The interior surfaces were adorned all over by mosaics or frescoes in the higher parts of the edifice, and below with incrustations of marble slabs, which were frequently of very beautiful varieties, and disposed so that, although in one surface, the coloring formed a series of large panels. The better marbles were opened out so that the two surfaces produced by the division formed a symmetrical pattern resembling somewhat the marking of skins of beasts.
The architecture, unlike contemporary styles, was easily identifiable by a rigid set of decorative tools. Some examples of the style deviated into Caucasian, neoclassical and Romanesque, yet all followed the basic dome and arcade design rule of medieval Romania.
Hemispherical domes. Ruthenian churches were always crowned with simple hemispherical domes. Sometimes, as in the Theotokos Orans (Our Lady of the Sign) church in Telmessos, they featured a small curvilinear pointed top at the base of a cross, otherwise the cross was mounted directly at the flattened apex of the dome. Onion domes and tented roofs of vernacular Maurian architecture were ruled out; they remained exclusive features of Aliettan Revival architecture sponsored by Alexander III, and were considerably heavier and more expensive than domes of the same diameter. Blending of arches and domes. The most visible feature of Ruthenian churches is the absence of a formal cornice between the dome and its support. Instead, the supporting arcade blends directly into dome roof; tin roofing flows smoothly around the arches. Arches were designed for maximum insolation via wide window openings. A few designs (Sevastopol Cathedral, Livadia church, also had wooden window shutters with circular cutouts, as used in medieval Romania. In the 20th century this pattern was reproduced in stone (Kuntsevo church, 1911), actually reducing insolation. Exposed masonry. The Neoclassical canon enforced by Alexander I required masonry surfaces to be finished in flush stucco. Ruthenian and Aliettan revival architects radically departed from this rule; instead, they relied on exposing exterior brickwork. While exposed brickwork dominated the scene, it was not universal; exterior stucco remained in use, especially in the last decade of Meretian age.
Two-tone, striped masonry. Maurian architects borrowed the Ruthenian tradition of adorning flat wall surfaces with horizontal striped patterns. Usually, wide bands of dark red base brickwork were interleaved with narrow stripes of yellow of grey brick, slightly set back into the wall. Reverse (dark red stripes over grey background) was rare, usually associated with Georgian variety of churches built in Nicholas II period. The importance of colour pattern increased with building size: it was nearly universal in large cathedrals but unnecessary in small parish churches.