Julius Caesar described the larger Celtic Iron Age settlements he encountered in Gaul as oppida and the term is now used to describe the large pre-Roman towns that existed all across Western and Central Europe. Many oppida grew from hill forts although by no means did all of them have significant defensive functions. Oppida surrounded by earthworks are known as enclosed oppida. The main features of the oppida are the architectural construction of the walls and gates, the spacious layout and commanding view of the surrounding area.
The development of oppida was a milestone in the urbanisation of the continent as they were the first large settlements north of the Mediterranean that could genuinely be described as towns. Caesar pointed out that each tribe of Gaul would have several oppida but that they were not all of equal importance, perhaps implying some form of hierarchy.
In conquered lands, the Romans used the infrastructure of the oppida to administer the empire and many became full Roman towns. This often involved a change of location from the hilltop into the plain.
In the mediaeval Kingdom of Hungary, oppidum was the legal Latin term for market towns (mezőváros in Hungarian), which were of lesser status than free royal towns but more important than villages.