The word "Lucilinburhuc" is synonymous with small fortress. The expression denotes two features which characterised the city for an extremely long time.
First of all, the rocky promontory obtained by Siegfried was of obvious strategic interest and gave itself admirably to fortification. The city of Luxembourg was to be a fortress city for almost a thousand years until being dismantled in 1867.
Secondly, it would never be a large city: there were 5,000 inhabitants at the beginning of the 14th Century, 8,500 by the end of the 18th century, 46,500 immediately after the First World War, and today there are 82,000 at the present day.
Siegfried was to build a veritable fortress on the promontory. Knights and soldiers were billeted there, while artisans and traders settled all around, the first group on top of the rocky outcrop and the others beneath it. Thus was created the distinction between the upper and the lower city. One is not able to talk of a proper city until the second half of the 12th Century, when it became surrounded by remparts of stone.
Certain cities owe their origins to a religious sanctuary, to an abbey, to the passage of a river, or to a crossing of the ways. Luxembourg owes its origins to its precipitous location and to the military interest which it thus provoked.