During the Iron Age, Celtic culture, deriving from the Hallstatt and La Tène cultures, arrived from Central Europe. Brythonic was the spoken language during this time. Society was tribal; according to Ptolemy's "Geographia" there were around 20 tribes in the area. Earlier divisions are unknown because the Britons were not literate. Like other regions on the edge of the Empire, Britain had long enjoyed trading links with the Romans. Julius Caesar of the Roman Republic attempted to invade twice in 55 BC; although largely unsuccessful, he managed to set up a client king from the Trinovantes.