An ancient building that predates Derry's walls has been discovered along with musket balls, a small cannonball and a number of intact wine bottles.
The building, believed to have been burnt down during a rebellion known as the O'Doherty rising, in 1608, had stone foundations, a cellar and upper floors made of timber.
The earliest find was a shard of medieval pottery dating to AD 1200-1400. Only a small part of the building has survived.
Environment Minister Mark H Durkan, has described it as highly significant.