Sigfried was count in the Ardennes, and is known in European historiography as founder and first ruler of the Castle of Luxembourg in 963 AD, and ancestor and predecessor of the future counts and dukes of Luxembourg. He was also an advocate of the abbeys of St. Maximin in Trier and Saint Willibrord in Echternach.

The Bock is a promontory in the north-eastern corner of Luxembourg City's old historical district. Offering a natural fortification, its rocky cliffs tower above the River Alzette, which surrounds it on three sides. It was here that Count Siegfried built his Castle of Lucilinburhuc in 963, providing a basis for the development of the town that became Luxembourg. Over the centuries, the Bock and the surrounding defenses were reinforced, attacked, and rebuilt time and time again as the armies of the Burgundians, Habsburgs, Spaniards, Prussians, and French vied for victory over one of Europe's most strategic strongholds, the Fortress of Luxembourg. Warring did not stop until the Treaty of London was signed in 1867, calling for the demolition of the fortifications. Ruins of the old castle and the vast underground system of passages and galleries known as the casemates continue to be a major tourist attraction.