Part 1 of Essay
Arch and Vault, a fundamental construction system in architecture used to span the space between walls, piers, or other supports and to create a roof or a ceiling. Until the 19th century the arch and vault were the only alternative to the far more limited and simpler post-and-lintel system supporting a flat or peaked beam ....

Part 2 of Essay
.... may be walls, piers, or columns, and the capstones from which it springs are known as imposts. The upper part of the arch is the crown, the portions near the impost are the haunches, its wedge-shaped segments are voussoirs, and the central or crowning voussoir is the keystone. The inner edge of the arch is the intrados; the outer edge, the extrados; and the undersurface, the soffit. The molded band that often is found around the opening of the arch is the archivolt. The wall spaces on either side of an arch, ....