Dorset's high chalk hills have provided a location for defensive settlements for millennia, with a large number of late Bronze Age but mostly Iron Age hill forts, such as Maiden Castle, Hod Hill, Badbury Rings and Hambledon Hill. The chalk downs were largely deforested during these times, making way for field and pasture. Some of the steeper slopes and hill tops are inaccessible or impractical for arable farming, and there the archaeology is relatively well preserved; the valley floors and broader hills have usually been ploughed, and hence do not have a good record of pre-Roman archaeology, although this does not mean that Iron Age peoples didn't settle there. Indeed, many contemporary theories postulate that hillforts may not have been the main focus of settlement, but served more as a marketplace-cum-stronghold in times of danger, and in fact most of the time, the population was concentrated in the valleys. By the Late Iron Age, the inhabitants of Dorset were minting their own coinage and thriving on trade with Northern Gaul (Armorica, now known as Brittany). However, after Armorica was conquered by Julius Caesar in 56 BC, the trade dried up; the Romans re-arranged trade with Britain to the profit of their allies, the Trinovantes, in Essex. The next century or so until the Roman conquest saw a long drawn-out period of economic retrenchment in Dorset, in parallel with a rising population and a decline in soil quality (much of it had been in cultivation for 4,000 years). By the time of the Roman Conquest, it is likely that a combination of overpopulation and impoverishment of the soil left many people starving, to which bone analysis of skeletons from Bere Regis bears witness; several of the skeletons present ample evidence of numerous distinct episodes of severe malnourishment during childhood.