The 47-year-old tourist from India was spotted by other visitors removing an entire brick from an inside wall after he detached from a tour group at the historic attraction, and reported to police.
While the brick was recovered and replaced, Rome's carabinieri today said the Indian tourist was “on the loose.”
Police want him for “damage and unlawful appropriation of cultural assets belonging to the state”, Il Messagero reports.
It's unclear what the punishment for this would be, but in the past other tourists have faced fines of several thousand euros for damaging the Colosseum.
The charge of defacing Italy's cultural heritage or landscape is punishable by up to five years in prison.
Vandalism has long been a problem at the iconic landmark, though it more usually takes the form of graffiti on the walls. However this man was not the first to try to take a piece of the Colosseum home.
Last month Rome brought in a raft of strict new laws to tackle unruly behaviour from tourists in the city, including a ban on ticket touts, street drinking, and eating near or climbing on fountains in the Eternal City.
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