The fortifications were built in the 5th century BC, corresponding to the early Celtic culture which would emerge as the Helvetii in Roman ethnography of the 1st century BC. The walls had a height of up to 14 m and a width of up to 35 m, enclosing a large settlement on the slope, with two inner rings of fortifications protecting the core areas, one at Aegerten-Plateau (now the site of the Üetliberg television tower), the other at Uto Kulm (now the site of the look-out tower). The fortifications presumably remained in use for more than four centuries, until the Roman conquest in the 1st century BC.