As in the Bronze Age, the coastal marshes were largely used as grazing for animals during the Iron Age, with a major salt industry based on the Red Hills of the Essex coast. These mounds are made up of the debris, especially a particular form of pottery made from red earth and known as briquetage, left behind by the process of evaporating sea water to make salt. The industry flourished in the Late Iron Age and during the Early Roman period.
The presence of a specific mineral in the clay used to make some of the pottery found at Little Waltham indicates that the clay itself was sourced from Maidstone in Kent, and it is likely that this represents a trade in pottery from Kent across the Thames to Essex. Similarly, a Glastonbury ware bowl from the West country was found at Heybridge. The fact that pottery was already being traded over large areas must have eased the travelling of imports from the Roman world before and after the invasion.
Trade between Britain and the Roman world increased in the late Iron Age, with imports of Italian wine evidenced by amphoras from Stansted and Heybridge, and Spanish wine at Thaxted in the first century BC (100-1 BC). The height of trade with Rome came with the reign of Cunobelinus in the first century AD (1-100 AD). Two bronze coins of Cunobelinus, found at Canterbury and in the river Colne at Colchester, bear images that corresond to Gaulish ships described by the Roman general Julius Caesar, and it seems likely that this type of ship had been seen on the Colne.