IN 1917, a Byzantine mosaic created during the reign of Emperor Justinian was removed by Australian troops from the ruins of a church near Gaza. The Australians knew they were plundering the priceless antiquity during World War I, two authors now claim.

In a new book, authors Paul Daley, a Sun-Herald columnist, and Michael Bowers, raise questions about Australia's continued possession of the mosaic, which has been in the Australian War Memorial collection since 1941.

''But from time to time, Australian authorities have privately expressed their unease at the fact that the mosaic was effectively looted from Palestine and removed to Australia, fearing it could become the focus of the type of debate that surrounds Britain's acquisition and 'safe keeping' of Greece's Elgin Marbles,'' Daley writes in Armageddon, Two Men on an Anzac Trail.

The Shellal Mosaic was uncovered and significantly damaged by Turkish soldiers while digging a machine gun position on a hill where the Shellal Church had once stood, according to the War Memorial. Anzac forces rediscovered the mosaic during the second battle of Gaza in April 1917.

In the book Daley, who disagrees with the government's view that not enough was known about the removal to determine if it was pillaged, describes how impressed Australian military leaders were with the find. In a letter to his wife, General Harry Chauvel wrote of the discovery of ''a very handsome mosaic floor''. Major-General Granville De Laune Ryrie wrote to his wife: ''It is done in different coloured little square stones set on cement and is awfully well done … the colours are very good, it would be worth a lot if it could be moved.''

A leading legal expert said the removal of an antiquity was a crime under international law.

''In a general sense [the soldiers] could be said to have violated the laws and customs of war,'' said Emeritus Professor Ben Boer from the University of Sydney's Law School. But Australia did not appear to be bound by these laws in April 1917, he added.

Professor Boer also said international law did not require the Australian government to return the Shellal Mosaic to its rightful owner.

The question of whether Australia should return the Shellal Mosaic is an ethical, not legal, one, he said. ''Should Australia return the mosaic in recognition of its importance to the cultural heritage of people of the region? However, it seems unlikely at this point that there would be a demand for its return.''

International law prohibits pillage, and the seizure of the property of institutions dedicated to the arts and sciences ''and breach of these provisions would amount to a war crime'', the Department of Foreign Affairs and Trade said.

However, it says that ''not enough is known about the circumstances of the removal of the mosaic to say whether or not it constituted pillage or seizure of property amounting to a war crime.''

A spokesman for Warren Snowdon, the Minister for Veterans' Affairs, said the Shellal Mosaic's remains were removed in the belief that it might be destroyed in future military action.

''The Australians who dug up the Shellal Mosaic knew its precise value. The Palestinian Authority is said to have carefully considered whether or not to seek some sort of formal acknowledgement from Australia that the mosaic rightfully belongs to its people,'' he said.

If there was such a request, then there could be a moral case for returning it, Professor Boer said.

But it may be impossible to return the item intact because it now forms part of a supporting wall.

''Because of its extreme fragility, any attempts to interfere with the Mosaic or try to detach it … will likely lead to its permanent damage,'' Mr Snowdon's spokesman said.

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