MEXICO CITY (AP) ― Mexico’s Senate has approved a measure meant to help win the temporary return from Austria of a headdress that was reputedly once owned by the last Aztec emperor.

Mexico had long held the view that all pre-Hispanic relics were national historic property and could not be exported, and that once they entered or returned to Mexico, they could not leave again.

The Senate’s unanimous vote confirmed a framework worked out between Mexico and Austria earlier this week to provide for temporary loans, while still recognizing the lender’s ownership rights.

The cultural exchange agreement with Austria could pave the way for an extended loan of the piece to a Mexican museum, but details of the loan must still be worked out, including how to protect the fragile headdress if it is moved.

The semicircle of green feathers from the Quetzal bird and other species is more than one meter wide, rather large for headgear.

Montezuma, the last Aztec emperor, gave the feathered headdress as a gift to Spanish Conqueror Hernan Cortes in 1519. But Mexican officials concede Montezuma probably never personally wore it.

Who it may have been made for, and whether it was ever actually worn on the head of some leader and in what situations, are still open to debate.

Cortes gave the headdress to Spain’s King Carlos V. It is not entirely clear how the relic made its way to Austria, but Carlos V had an Austrian connection as part of the Hapsburg line, and he held other titles, including Holy Roman Emperor and Archduke of Austria.

Mexico has tried for decades to win the return of the headdress, at one point appealing the case to the United Nations.

Mexican officials have said that in exchange for the headdress they could loan Austria the ceremonial carriage used by Emperor Maximilian, a member of the Austrian royal family who was imposed as Mexico’s ruler by a French invasion. He ruled from 1863 until he was deposed and executed in 1867.