It is a spectacular work of art and a highlight at Mexico's National Museum of Anthropology.

The semicircle of gleaming green feathers held together by rows of golden beads was, it is said, the headdress of Mexico's last Aztec ruler, Moctezuma.

But the spectacular artefact is not real - it's a replica. The original lies thousands of kilometres away in a collection at Vienna's Ethnology Museum.

The exact origin of the headdress or "penacho" is disputed but one version says Moctezuma gave it to the Hernan Cortez, leader of the Spanish conquistadors, in the 16th Century. By the twists and turns of history, it ended up in Austria.

Nearly 500 years on, the original may be loaned temporarily to Mexico, a development that has created expectation there and highlighted the country's historic riches.

But the pre-Hispanic artefacts and sites not only attract tourists; looters and traffickers see a chance to profit from the wealth of the past.

Now the authorities are looking at various ways of clamping down on this trade in relics of their nation's history....