Structure

The structural systems roughly parallel the principal architectural components: the primary space of the nave and the enveloping secondary spaces of narthexes, aisles and galleries. Sustaining the dome and other high vaults over the nave are chiefly the main piers, the secondary piers and the buttress piers, and groups of arches spanning between these piers. The primary structural system certainly comprises all of these, as well as the dome and vaults themselves. The secondary systems might be defined as comprising all other structural elements of the church-proper. They thus include the arches and the vaults of the narthexes, and the main bays of the aisles and galleries, and all their supporting walls and columns that’s are not part of the primary system. The colonnades are regarded as parts of both systems- the side colonnades belonging chiefly to the secondary system.