Rome , Italy ( CNN ) -- Visitors to a popular tourist destination in Rome should soon get their first look at a once-formidable world that has been hidden from public view for nearly 2,000 years . For the first time , the Colosseum plans to let visitors explore an underground corridor that has previously been off limits . It 's a place where gladiators once prepared for battle and lions and tigers were caged before entertaining a bloodthirsty public , architect Barbara Nazzaro of the office of the Rome Archaeology Superintendent told CNN . The Colosseum plans to open the underground section in August . In the underground maze of tunnels , the Romans kept `` every type of exotic animal that they were able to bring here , '' including rhinos and snakes , Nazzaro said . Elephants and other animals could walk freely without scraping their head on the ceiling -- with plenty of room to spare . Completed in 80 A.D. , the Colosseum once held 50,000 to 60,000 people and reached an impressive 130 feet in height . It was constructed with enough stone to build a 15-story building , though less than half of the structure now remains , said Nazzaro . For more than 400 years , wealthy and poor alike attended ultra-violent spectacles in the Colosseum , including executions which often concluded with fights between Roman warriors . There were four floors , each dedicated to a specific class , according to colosseum.net , a website dedicated to amphitheaters and coliseums around the world . The upper floors were for the lower classes and women , while the lowest was for the most prominent citizens , sitting just above the underground passageways . The more gore and blood , the happier and more involved people became , Nazzaro said . `` It is difficult to understand nowadays . '' Listed as one of the seven wonders of the world , the Colosseum requires the equivalent of more than $ 860,000 a year ( 700,000 euros ) to maintain , according to the archaeology superintendent 's office . Opening the underground corridor for the public will coincide with an extensive restoration of the Colosseum , the office said . It will cost an estimated $ 2.5 million ( 2 million euros ) to open the new attraction to tourists . Yet restoration plans do n't stop there . Efforts to find sponsors to help fully restore the entire Colosseum , including more of the underground section , are underway . That could cost the equivalent of another $ 40 million ( 32 million euros ) , officials said . The Colosseum attracts an estimated 4 million tourists a year and generates roughly $ 38 million ( about 30.5 million euros ) in revenue from such things as ticket sales and souvenirs , according to the archaeology superintendent 's office .
Colosseum plans to open underground section in August . Romans once prepared for battle in passageways . Animals also kept in underground section .