 (Later, in the mid-Roman period, probably in the 3rd century, a change took place in that the round structures were replaced by rectilinear buildings on some sites).Most of the population, the total size of which at its peak has been estimated at between 20,000–30,000 people, lived in scattered communities, usually consisting of just a single family group.They practised mixed agriculture, with enclosures for arable use, but also with enclosed and unenclosed pasture fields.