Hailed as the birthplace of the city, excavations on the site of Sheffield Castle have revealed archaeological features and structures that heat up the city’s industrial heritage.

The 10-week dig is part of Sheffield City Council’s Castlegate regeneration project. The excavation, overseen by construction engineering specialists Keltbray, will uncover and preserve the castle’s imposing medieval gatehouse.

Like most excavations, it all starts with a map - and for this part of the site, on top of castle hill, it’s the 1850s Ordnance survey map and some important research questions which drive us.

1850s OS Map showing steel works on site of Sheffield Castle

1850s OS Map showing steel works on site of Sheffield Castle ©National Library Scotland

Reaching the first archaeological horizon

Having removed the modern concrete foundations of the former market and some of backfill deposits beneath it, a few structures began to emerge. We had reached the first archaeological horizon and were firmly in the 19th century.

As we got to work carefully removing the loose rubble infill surrounding the structures, a few bricks were left hung in the air, the remnants of a vaulted ceiling. After carefully recording these remains we dug deeper and were surprised to find that the cellar was that of a crucible furnace. Distinctive rows of brick bays were unearthed - the remains of ash or ‘rake out’ pits below the furnace. These furnaces would have been used to refine blister steel into higher quality crucible steel. Suspecting that there would be stairs somewhere we set out to dig in a likely spot and revealed four curving steps descending down to the cellar. The steps are shown on the 1850s Ordnance Survey map, but came as a surprise on the ground as the base of the steps had been bricked up. The furnace was previously unknown and does not appear on consulted maps.

This cellar would have been a hot, unpleasant place when the crucible furnaces above were working. Reaching temperatures of 1200 degrees centigrade, the firing process was hot and efficient, but it also produced lots of ash which needed to be cleared. The ash would fall into the ‘rake out’ pits below, where a worker, perhaps a young boy, had the back-breaking job of removing it.

Crucible bays

Rake out pits from a former crucible furnace extend east-west ©Wessex Archaeology

During the initial machining of the demolition layers, archaeologist Marijane Porter excavated a Sondage (a type of deep trial trench in a small area to confirm the deposit sequence) down through the cellar backfill.

As we troweled further down, there was a thin dark layer of clay overlying waste material from the firing process right by the rake out pits.

Marijane Porter Archaeologist


Having dug through a dark black clay layer towards the base of the floor of the furnace we found loads of pieces of ceramic fused together- one of the volunteers suggested it might be part of some sort of vent or cowl– but we won’t know more until it’s processed by our finds specialists!

Curious fused ceramic find Curious fused ceramic find

This curious fused ceramic find will go to our specialists for identification ©Wessex Archaeology

Unmapped furnaces survive on castle mound

Finding the remains of crucible furnace like this is really exciting not only does it show that unmapped furnaces survive on the castle mound, it begins to tell the full picture of the steel working process - which is one of our research aims for this excavation.

In the 2018 trial trench evaluation, we found parts of a cementation furnace which would have produced blister steel. Blister steel was refined in a crucible furnace to produce a higher quality more homogeneous product so finding the two furnaces from the same works may be evidence of processes and workflow at the Castle Hill Steel Works.

Archaeologist record industrial features

Archaeologists Isabelle Sherriff and Aaron Friar record the furnace structures ©Wessex Archaeology

As we undertake the final stages of systematically recording the furnace, our next step is to go deeper into Sheffield’s rich archaeological past.