Archaeologists have discovered a large, heavily-fortified structure containing 33 musket balls while investigating the Royal Fort in Bristol.
The team made the discovery during a ten-week dig.
The building measures in excess of 25 metres in length and has several window openings or embrasures.
Also found was a subterranean structure measuring over five-metres square and several metres deep which could have been used to store munitions.
Artefacts including a cannon ball, lead caps from gunpowder flasks and parts of two leather shoes from the ditch of the fort were also found.
Bruce Williams, from the Bristol and Region Archaeological Services said: "The excavations have helped to re-write our knowledge of the Royal Fort, in particular the scale of the fortified structures within its walls."
The Royal Fort, next to the University of Bristol's HH Wills Physical Laboratory, is one of the most significant fortifications from the English Civil War.
The fort was held by royalists until 1645 when it was surrendered to Oliver Cromwell. It was largely destroyed in the 17th and 18th Centuries.
The fort was designed by Sir Bernard de Gomme to defend Bristol and to act as western headquarters for the Royalist Army under Prince Rupert.
It was surrendered along with the city in September 1645 to Oliver Cromwell and his New Model Army.
Pictures courtesy of the Bristol and Region Archaeological Services (BaRAS).