The burial site on Ridgeway Hill near Weymouth is thought to date from late Iron Age to early Roman times.
Skulls, rib cages and leg bones, thought to be from young men, were arranged in separate parts of the pit.
Archaeologists said they appeared to have been victims of a "catastrophic event" like an execution or disease.
The skeletons were discovered during the earthwork operation for the Weymouth Relief Road.
David Score, Oxford Archaeology project manager at dig, said it was a "remarkable burial pit".