Contraband also includes a black market economy of Mayan, Aztec, and ancient civilization artifacts.
This market is created because of the lack of government funding for excavating newly discovered sites.
For example, if someone buys land in an undeveloped forest they might come upon an ancient site. The law requires them to stop developing the land immediately and report the site to the government. Then, wait until the government excavates the site -which would be typically years, if ever.
Because of this, most will simply tomb raid and the relics end up in a black market economy which is mixed with knock offs in an attempt to liquidate them to "rich" tourists.
Smugglers also will try to get them into the U.S. for their private clients.
There are treaties between many nations that require the return of the nation's artifacts if they are found in the United States, but enforcement of penalty is lax given that many of these nations have poorly developed diplomatic relations with the States who essentially Bully them because they can.
I took this photo of a spice bowl.