The Pantheon in Rome is one of the oldest and most well-preserved ancient structures still standing today. Originally built as a temple to honor all gods in 27 BC, it was later reconstructed under Emperor Hadrian in 125 AD and converted to a Catholic church in 608 AD. The Pantheon's most distinctive feature is its large oculus opening at the top of the dome, which at nearly 30 feet in diameter was the building's only source of light. Though originally used as a pagan temple, it continues to serve as a Roman Catholic church and is still an iconic landmark attracting many visitors to Rome.