19 CFR 12.107: Importations permitted.

Pre-Columbian monumental or architectural sculpture or mural for which entry is sought into the Customs territory of the United States will be permitted entry if at the time of making entry:

(a) A certificate, or its electronic equivalent, issued by the Government of the country of origin of such sculpture or mural, in a form acceptable to the Secretary, certifying that such exportation was not in violation of the laws of that country, is filed with the port director; or

(b) Satisfactory evidence is presented to the port director that such sculpture or mural was exported from the country of origin on or before June 1, 1973; or

(c) Satisfactory evidence is presented to the port director that such sculpture or mural is not an article listed in § 12.105.