The Colosseum arena, showing the hypogeum now filled with walls. The walls were added early in the Colosseum's existence when it was decided it would no longer be flooded and used for naval battles. (Source)
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A view of the interior of the Colosseum; clearing showing the hypogeum (Greek for "underground") (Source)
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Ave Imperator, morituri te salutant (Hail, Cesar, those who will die salute you), by Jean-Lon Grme, 1859 (Source)
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Pollice Verso (Thumbs Down) by Jean-Lon Grme, 1872 (Source)