The heavy metal from the south that helped power the Roman Empire

• Report by ITV Meridian's Derek Johnson

Down a woodland path and under a canopy of trees a fascinating experiment is taking place.

A clay furnace is being topped up with charcoal and is spewing out flames. It’s being heated up in a process very similar to one carried out across the Weald of Sussex and Kent before and during Roman times.

The furnace is part of a camp in Ashdown Forest built by the Wealden Iron Research Group, set up to study the long-extinct iron industry of Sussex, Kent and Surrey. And to replicate what the Romans did 2,000 years ago.

"The iron we make is a solid, spongey iron,’" says group member and retired metallurgist Tim Smith. ‘’It’s what we call a bloom. So it’s never molten.

"The only molten material is the waste material, the slag, that flows out of the furnace. We use a tapping procedure to get it out and to allow the iron to form."

In later centuries the Weald would again be Britain’s main iron producer with the invention of more sophisticated and permanent blast furnaces.

Originally though the area was chosen because of the abundance of wood which was used to make the most important ingredient, charcoal. Also found in abundance was iron ore, a product of the Wealden geology of sand and clay. Plus there was plenty of water for the workers.

The charcoal and ore were put into the furnace, which is about a metre high and with thick walls. The mix was heated for hours, with air from bellows being blown into the furnace - charging material within and turning it into metal iron. 

Our volunteers have a bit more help than the Romans had. Temperature gauges and an electric pump. The alternative, which is what used to happen of course, is people using hand-powered bellows.

Iron was made long before the Roman invasion and occupation. 

Group member Jeremy Hodgkinson said: "There had been an iron industry in the Weald since as long ago as the third or even fourth century BC. When Julius Caesar came to Britain for the first time in 55 BC and then again in the next year, he mentioned that the Britons made iron in a small way in the maritime parts.

"We take that to probably mean the coastal part of the Weald around near Hastings. And then probably a few decades later a Greek geographer wrote that among the exports of the Britons was iron. So clearly there had been an upscaling of the industry at that time in the pre-Roman period, possibly associated with the growth of Roman Gaul (France) across the Channel and maybe there was a market for iron that was being produced in the Sussex Weald and exported across the Channel."

In fact the Romans may have exported an astonishing 30,000 tonnes of iron from this part of Southern England over 150 years. 

Jonathan Pruce from the Historical Metallurgy Society said: "Really it’s the scale on which it was done that was unprecedented. Before the Roman occupation the iron production sites that we find are really quite tiny. It’s a cottage industry. But the Romans managed to organise enough people and resources to produce huge amounts on single sites.

"There was also plenty of room for an iron industry. The soils in the Weald were so poor that the land hadn’t been overused for agriculture."

The reason for the massive expansion is that the Empire needed iron to sustain itself. Not just for practical goods such as tools, nails and horseshoes which could be traded far and wide. But also for armour and weapons for the many Armies.

There are signs the industry would have been under tight control by the military. The Roman fleet took a key role in iron production and export.

Landscape archaeologist Judi English said: "What you don’t find is any evidence of great wealth. And the suspicion is that this is very much under price control. The Romans are not paying a high price. They are not enabling local civilians to get rich and to build villas. That simply doesn’t happen. There is one suggestion in fact that the Weald was an Imperial state. Difficult to prove but we do have the presence of the fleet so the Roman military are here. And they would essentially turn the local people into slaves."

As for our own forest furnace, after a full day of burning and blowing there is bloom produced. It is quickly cooled and hammered as part of the slow process of extracting metal and creating iron. The group is not always so lucky. Some days are less successful than others although members will carry on experimenting.

Jeremy Hodgkinson said: "We will continue to research it, look for sites and find the ways in which they made it by the most efficient method. Obviously they were a lot better at it than we are in terms of the primitive techniques. We just want to know more. There’s more to find out."

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