Discovered: Stone Age man's morning after the night before

Archaeologists in Wiltshire have discovered remarkable evidence of a spectacular party – enjoyed by Neolithic tribesmen 4,500 years ago.

Excavations at Britain's biggest "henge" site – a prehistoric religious complex 16 times the size of Stonehenge – have yielded the remains of dozens of pigs slaughtered for an ancient ceremonial feast.

The archaeologists, from English Heritage, also discovered the remains of a temporary Neolithic ritual building which they believe was constructed specially for the event – probably for staging religious feasts and rituals. The 25sq m timber structure was surrounded by hundreds of discarded pig bones. It's one of the very few Neolithic buildings ever discovered in Britain.

Built on top of the earthwork bank of Marden Henge's previously unknown inner sanctum, the building overlooked the river Avon. The archaeologists – led by English Heritage prehistorian Jim Leary – believe that the river was sacred to the prehistoric population of the area.

Other finds being unearthed at the site include high-status decorated pottery, ultra-rare bone implements – and an elaborate ceremonial flint arrow head. "The new discoveries are of international importance because the material being unearthed is extraordinarily rare and will shed unprecedented new light on religion and ritual in Neolithic Britain," said Mr Leary. "The excavation is exceeding all expectations. It is likely to change prehistorians' understanding of Britain's henge monuments."