The 337 pieces displayed in the ancient Roman arena include vases, bronze tools and marble statues of Venus, some dating as far back as the 8th century B.C.
Police said the pieces are worth some euro15 million (about $20 million) overall. They said the pieces were returned from Switzerland in June after a two-year investigation.
Italy has aggressively pursued the return of art it says was illegally looted from its soil and sold to museums or private collections worldwide.
This probe grew out of an investigation into an Italian art dealer later convicted of art trafficking.
The objects were seized in Geneva, part of a massive haul of some 20,000 artworks from all around the world, the art squad of the Carabinieri police said.
The pieces returned to Italy also include “kraters” — huge vases used to mix wine and water — statuettes and drinking cups. Police say the objects were looted mostly from southern Italian regions and, after their spectacular display Friday at the Colosseum, they will return there.