As sanctioned Russian oligarchs’ assets are detained or frozen around the world, many free ports — vast warehouses used by the super-rich to store art and valuables, tax-free — have stayed largely below the radar, at least for now.

Might that change if the sanctions ring continues to tighten? "I assume (questions) will come eventually,” says Fritz Dietl, president and founder of Delaware Freeport LLC, who says he has yet to be contacted by law enforcement agencies of any kind regarding assets potentially owned by sanctioned Russians. "But when it comes, and if it comes through the proper channels, then we’ll answer the authorities.”

Free ports are not new. Ports Francs et Entrepots de Geneve, known both as Geneva Freeport and Free Port, is the world’s biggest; it capitalized on Switzerland’s neutrality to distribute Red Cross parcels to prisoners of war across Europe during World War II.