The loot hasn't been recovered. It includes a diamond-and-emerald necklace Napoleon gave to Empress Marie-Louise, jewels tied to 19th-century Queens Marie-Amélie and Hortense, and Empress Eugénie’s pearl-and-diamond tiara.
The robbery has focused attention on security at the Louvre, the world's most-visited museum.
The thieves took less than eight minutes to force their way into the museum and leave, using a freight lift to reach the building's window. Footage from museum cameras showed two broke into the ornate Apollo Gallery, cutting into the jewelry display cases with disc cutters and making off with the trove, while two riders on scooters whisked them away.