Pre-Celtic tribes inhabited Portugal leaving a remarkable cultural footprint. The Cynetes developed a written language, leaving many stelae, which are mainly found in the south of Portugal. Early in the first millennium BCE, several waves of Celts invaded Portugal from Central Europe and intermarried with the local populations to form several different ethnic groups, with many tribes. The Celtic presence in Portugal is traceable, in broad outline, through archaeological and linguistic evidence. They dominated much of northern and central Portugal; but in the south, they were unable to establish their stronghold, which retained its non-Indo-European character until the Roman conquest. In southern Portugal, some small, semi-permanent commercial coastal settlements were also founded by Phoenician-Carthaginians.