Zürich has been continuously inhabited since Roman times. The vicus of Turicum was established in AD 90, at the site of an existing Gaulish (Helvetic) settlement. Gallo-Roman culture appears to have persisted beyond the collapse of the Western empire in the 5th century, and it is not until the Carolingian period. A royal castle was built at the site of the Lindenhof, and monasteries are established at Grossmünster and Fraumünster.