Italy has announced plans to build a retractable floor at the Colosseum in Rome and has issued a request for bids for carry out the €18.5m ($22.5m) reconstruction project.

When it was inaugurated in AD 80, tiered seating encircled the 50,000-seat Colosseum, which had a wooden, sand-covered floor. It was built over an underground complex where wild animals were caged and stage sets prepared, and crowds gathered to watch gladiators fighting the animals or each other. The last battles were fought there in the fifth century AD, and Rome’s great gladiatorial arena is now Italy's top visitor attraction.

The Colosseum has been without a floor for 1000 years, and thus the labyrinth of secret tunnels, or ‘hypogeum,’ has been on view to visitors for more than a century. Work is expected to start next year on the new retractable floor, which is expected to feature trap doors and hidden lifts. The country's culture ministry has revealed that the redesigned floor must be able to close quickly to protect the underground spaces from rain.