The Gaulish ethnonym Leuci (sing. Leucos) literally means 'the bright ones, the lightning ones'. It stems from the Proto-Celtic *lowkos ('light, bright'; cf. Mid. Irish luach 'glowing white', Middle Welsh llug 'eyesight, perception'), itself from Proto-Indo-European *leukós ('bright, shining'; cf. Lat. l?x 'light', Grk leukós 'white', Toch. ly?ke 'light').
The territory of the Leuci extended in the east and the south-east up to the Vosges mountains, between the Marne and Moselle rivers. They were located north-west of the Sequani, and south-west of the Mediomatrici.
During the Roman era, their capital was Tullum (modern Toul). Ptolemy (2nd c. AD), who normally gives one capital for each civitas, also lists Nasium (present-day Naix-aux-Forges) as a capital of the Leuci.
Hillforts held by the Leuci included a large oppidum at Boviolles (Ornain valley) west of their territory, and some small ones in the Vosges. The Roman-era successor of Boviolles was more opposing that the capital Tullum, since the Ornain river was important trade route between Champagne and the plateau of Langres, on the territory of the Lingones. Another possible oppidum was located at Geneviève (Essey).