We review the systematics of the tetragnathid spider genus Sancus Tullgren, hitherto known from a single species from Kilimanjaro. The type species Sancus bilineatus Tullgren is redescribed and diagnosed from the only other known species, S. acoreensis (Wunderlich) new combination. Leucognatha Wunderlich is a junior synonym of Sancus, which thus eliminates two monotypic tetragnathid genera. A phylogenetic analysis of 15 tetragnathid and eight outgroup genera confirms the monophyly of Sancus and places it precisely in Tetragnathidae. We discuss the phylogenetic relationships among tetragnathid genera and the peculiar biogeography of Sancus, now known from east African mountains (Kilimanjaro and Mt. Kenya) and from the Azores in the northeastern Atlantic.