Byzantine architecture diverged from Late Roman architecture beginning in the 7th century, acquiring distinctive characteristics. In this body of architecture, the so-called ‘cross-in-square’ churches offer characteristic examples. Many previous studies have classified the cross-in-square into various sub-types, mostly based on variations in their plan, while few studies have discussed the relationships among the sub-types or possible chronological development. In this context, this paper aims to investigate the chronological transformation of the cross-in-square from 9th to 12th centuries, or Middle-Byzantine period, using as many churches as possible whose three-dimensional information is available (95 churches; Fig. 3; Table 1).
First, the churches were categorised into 17 types based on the wall part: according to the arrangement of arches and the number of the highest arches (Fig. 4), the shape (horizontal section) of the supports (Fig. 5), the number of the bays in the churches and the methods by which the arches and supports are connected (Fig. 6). Then, the churches were categorized into 11 types based on the ceiling part: according to the way the arches were arranged and the number of the highest arches, the number of ceilings and the number of transverse arches at the western and the eastern corner bays (Fig. 7). In total, 24 categories emerged from a combination of the wall and ceiling elements.
Then the features of each category were labelled according to the arrangement of arches and the number of the highest arches, e.g., the Arch-8 pattern, the Arch-4 pattern, the Arch-6 pattern, the Arch-2 pattern, the Arch-2’ pattern and the Arch-2(wall) pattern. Through the comparison, two lineages of these categories were distinguished, along with an additional group where the relationships among the elements were not clear but where the overall architectural configuration was similar. One lineage consisted of churches with 12 bays and ceilings, where all arch heights were the same, the horizontal sections of the supports were round, the supports and the arches were discrete, each corner bay had two transverse arches and the corner bays were covered with cross vaults or domical vaults (Aα-type; Fig. 10, upper). The other lineage came from the churches with 9 bays and ceilings, where north-south arches were higher than the other arches, where the horizontal section of the supports were quadrangular, where the supports and the arches were continuous, and where each corner bay had one transverse arch while the corner bays were covered with barrel vaults (Gδ-type; Fig. 10 bottom). The former lineage changed over time, decreasing the number of bays and ceilings, changing the horizontal section of the supports from round to quadrangular and eliminating the use of transverse arches, while the latter lineage changed by quadrangular horizontal sections with circular ones, decreasing the number of transverse arches from one to two and increasing the number of bays (Fig. 9). The planning pattern of these churches therefore tends to converge over time: previous sub-types (as shown in Fig. 1) overlooked such chronological changes, as they do not focus on three-dimensional characteristics of the structures and mixed architectural configurations (Fig. 9).
In short, this paper shows the chronological transformation of the cross-in-square churches and their distinct lineages in terms of the interior architectural configuration, which previous studies simply grouped as cross-in-square and regarded as largely unchanging because of their focus on the architectural plan alone.