Carolingian architecture in the context of "Westwork"

50°46′32″N 6°05′02″E / 50.77556°N 6.08389°E / 50.77556; 6.08389

The Palace of Aachen was a group of buildings with residential, political, and religious purposes chosen by Charlemagne to be the center of power of the Carolingian Empire. The palace was located in the heart of the current city of Aachen, today in the German Land (or state) of North Rhine-Westphalia. Most of the Carolingian palace was built in the 790s but the works went on until Charlemagne's death in 814. The plans, drawn by Odo of Metz, were part of the program of renovation of the kingdom decided by the ruler. The Palatine Chapel that was part of the palace complex has been preserved and is considered a masterpiece of Carolingian architecture and a characteristic example of architecture from the Carolingian Renaissance. Also, the foundations and lower walls of the Aula Regia (council hall) are preserved in the current town hall as are the first three stories of its square tower (so-called Granus Tower).

A groin vault or groined vault (also sometimes known as a double barrel vault or cross vault) is produced by the intersection at right angles of two barrel vaults. The word "groin" refers to the edge between the intersecting vaults. Sometimes the arches of groin vaults are pointed instead of round. In comparison with a barrel vault, a groin vault provides good economies of material and labor. The thrust is concentrated along the groins or arrises (the four diagonal edges formed along the points where the barrel vaults intersect), so the vault need only be abutted at its four corners.

Groin vault construction was first employed by the Romans, but then fell into relative obscurity in Europe until the resurgence of quality stone building brought about by Carolingian and Romanesque architecture. It was superseded by the more flexible rib vaults of Gothic architecture in the later Middle Ages. Difficult to construct neatly because of the geometry of the cross groins (usually elliptical in cross section), the groin vault required great skill in cutting stone to form a neat arris. This difficulty, in addition to the formwork required to create such constructions, led to the rib vault superseding the groin vault as the preferred solution for enclosing space in Gothic architecture.