By 650, the Franks were establishing themselves as overlords, which is suggested by archeological evidence of burials, and were building fortifications in various places including Christenberg. By 690 they were taking direct control over Hessia, apparently to counteract expansion by the Saxons, who built fortifications in Gaulskopf and Eresburg across the river Diemel, the northern boundary of Hessia. Büraburg (which already had a Frankish settlement in the sixth century) was one of the places the Franks fortified in order to resist the Saxon pressure, and according to John-Henry Clay the Büraburg was "probably the largest man-made construction seen in Hessia for at least seven hundred years". Walls and trenches totaling one kilometer in length were made, and they enclosed "8 hectares of a spur that offered a commanding view over Fritzlar and the densely populated heart of Hessia". The presence of a mounted garrison is deduced from archeological finds, including spurs, harness fittings, and fragments of weapons.