Where there is no lantern, the vault of the crossing is generally a continuation of that of the nave or transepts. It is, therefore, often of simple four-part cross-ribbed type, with or without a domed up crown.[331] Certain of the Gothic builders, however, even in the early thirteenth century, realized the advantage to be gained by subdividing the cells of the crossing vault with ridge ribs. Hence in the abbey church of Fossanova (consecrated in 1208),[332] as well as in those at Casamari and Arbona[333] in Italy, and in many churches of France,[334] especially those of Anjou type,[335] transverse and longitudinal ridge ribs were used and in most instances the vault was considerably domed up. In Amiens cathedral (cir. 1265) the crossing vault, nearly forty feet square and about one hundred and forty feet from the ground, was further subdivided by a single pair of tiercerons in each of the major severies, and the eight central panels thus formed were raised at the crown to reduce the thrusts of the vault as well as the amount of centering necessary for its construction. After its introduction at Amiens this form of crossing was quite extensively employed, sometimes with its ridge ribs running completely across the bay, as for example, in Auxerre cathedral, sometimes running only to the keystone of the tiercerons, as in Bayonne and Troyes cathedrals or Saint Euverte at Orleans. With the use of many added ribs in other portions of the church, came a corresponding elaboration in the vaults of the crossing. Thus many examples might be cited of lierne and tierceron vaulting in all degrees of complexity, especially in England,[336] while fan vaulting is to be seen in the abbey church of Bath (cir. 1500-1590),[337] and pendant vaults of elaborate character in Saint Étienne-du-Mont at Paris (probably cir. 1550-1600). Occasionally also the transept is subdivided by a central row of piers in which case the vault of the crossing is in two bays.[338] It is unnecessary, however, to discuss at length these exceptional crossing types since they do not differ structurally from the vaulting systems already described in connection with the nave. CHAPTER III APSE VAULTS The traditional method of terminating the church edifice at the end reserved for the clergy was by means of a semicircular or polygonal apse, and this method, which was of Roman origin, continued to be followed in the majority of Romanesque and Gothic churches. Such apses gave to the interior of the edifice a more dignified appearance than was possible with a flat east wall, by avoiding the abrupt termination which the latter produced and by emphasizing the central point in the sanctuary, which was occupied by the high altar in most of the mediaeval churches. APSES VAULTED WITH HALF DOMES