Celtic tribes, with origins in the Danube basin, settled in the Ardennes hills and surrounding plains from at least 1000 BC. The Romans advanced north into the region (then part of Gaul) from around 50 BC and controlled much of it over the next five centuries from garrisons such as that at Trier. Frankish clans from the middle Rhine valley spread across present-day Luxembourg from around the 5th century AD and intermarried with the Gallo-Romans. Anglo-Saxon missionaries were active in the region during the 7th century, and a Benedictine monastery was founded at Echternach in 698. From the early 9th century the region was controlled by Charlemagne, the Roman Emperor in the West, who ruled from Hungary to the Atlantic Ocean. The empire’s division, following the signing of the Treaty of Verdun in 843, enabled the rise of several feudal states, one of which became Luxembourg; the castle of Lutzilinburhurch was founded by Count Sigefroi in 963 on an outcrop overlooking the river Alzette.