The driving principle underlying this change was the acceptance by bishops, more or less willingly, of an imperial invitation to adopt and maintain the duties, dignity and insignia proper to a public magistrate.[4] Characteristically a Roman magistrate presided from a raised throne in a large, richly decorated and aisled rectangular hall called a basilica; and now bishops would do the same. The earliest of these new basilican cathedrals of which substantial remains are still visible (and maybe amongst the very earliest to be built) is below the Cathedral of Aquileia on the northern tip of the Adriatic sea. Dated from a mosaic inscription between 313 and 319, the complex consisted of two parallel east–west aisled halls of similar size; with a third smaller north–south cross-hall connecting them, which has been interpreted as the presence hall of the episcopium or bishop's residence.