Tortures were among the gruesome spectacles staged for the 12,000 people who attended performances at the Roman amphitheatre in Chester some 2,000 years ago, according to new evidence.

A gladiatorial torture block has been discovered in the centre of the arena, which was once the largest in Roman Britain.

The huge stone slab, with an iron fitting fastened into the surface, would have been used for chaining victims during spectacles.

The find has astonished archaeologists, who now realise that two similar stones found in 1975 had been completely misinterpreted until now. They were believed to have simply marked a processional path.

Their real purpose was confirmed by an image of such stones in a mosaic of gladiators found at a Roman villa at Bignor, West Sussex, in the 19th century.

The new evidence proves that gladiatorial activities at an amphitheatre thought to have been modelled on the Colosseum in Rome went way beyond ceremonial military displays.

Whether the victims were human or animal is unclear at the moment. One theory is that the blocks were used for executing criminals, who would be cast into the arena together with violent beasts. Archaeologists say that spectactors may also have been treated to a fight between chained bulls and bears.

The stone was found about 13 feet (4m) below ground, during the final stage of a three-year excavation by English Heritage and Chester City Council.

Dan Garner, one of Chester’s archaeologists, said that previous theories suggesting the arena was used for military tattoos or drill practice could now be “firmly banished”: “I dare say that people met a rather brutal end in Chester’s arena some 1,900 years ago.”

Tony Wilmott, an archaeologist with English Heritage, said: “What is certain is the Romans’ flair for mass entertainment. By chaining victims to these blocks along the long axis, they are trying to make sure that spectators have the maximum view of whatever was happening and preventing victims from sheltering against the arena wall, where they could be seen by only half of the audience.”

The amphitheatre was rediscovered by chance in 1929, having disappeared from sight in the 14th century. Although it was once one of the larger arenas in Northern Europe, little of it has survived.

Half of the remains are buried beneath the site of an 18th-century building. Most of the original stones were used to build the city walls and the adjacent church in the 11th century.

The discovery will be presented at an international symposium, entitled Roman Amphitheatres and Spectacula: a 21st century perspective, to be held in Chester this weekend.

Archaeologists will learn how the excavations have revolutionised what was known about the amphitheatre, shedding fresh light on its architecture. Evidence shows that it once had eight vaulted stairways serving as entrances.

Mr Wilmott, who is chairing the symposium, said: “Further analysis of the architectural scheme according to classical proportions has enabled English Heritage to reconstruct the height and grandeur of the amphitheatre. It shows that it had a highly elaborate, two-storey stone decorative treatment on the exterior, which is extraordinary and seldom found north of the Alps. Its closest parallels are the Colosseum itself in Rome and the amphitheatre of El Djem, Tunisia.”

He said the findings would change the way historians thought not only about Roman Chester but also about the social and cultural meaning of amphitheatres and spectacles across the Roman empire.

Other finds have revealed that the spectators — mostly made up of the thousands of le-gionnaires stationed at Chester — would have tucked into ribs and chicken while watching the tortures and other spectacles. Tiny bowls decorated with images of gladiators suggest that the spectators also liked to have a souvenir of a good day’s torture.