The remains of Scotland's ancient floating houses, built on the lochs and inhabited from the Bronze Age to the 17th century, are for the first time being studied under water, with techniques used during the raising of the Mary Rose.

Up until now little was known about these oak houses, called crannogs, and still less about their inhabitants. Built on stilts several metres above the water, they were unattached to the shore and safe from attack.

The Scottish Trust for Underwater Archaeology, founded by Nick Dixon, research fellow at Edinburgh University, has used underwater excavation techniques to explore the sites. All previous excavations have been in drain lochs or of what has survived above water.

Undisturbed for centuries and preserved in the freezing peaty waters of Loch Tay, Oakbank crannog is the most complete site so far explored. Dr Dixon said: "We discovered the remains of a Bronze Age house floor. Nearby we found many of the objects people used in their every day lives. There is pottery with burnt food still sticking to the inside."

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But further excavations are dependent on funding. With the help of charitable grants the trust has begun to build its own crannog to provide a research centre and a vital source of income.

Barrie Andrian, a trust director, said: "We had found so much structural evidence we could build an accurate replica. The process of building allows us to answer several questions about the structure. Ultimately we plan to have a visitor's centre and will run activities to teach children and adults about how these people lived."

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The replica crannog will not be complete until Easter 1996, when it will be opened.

It is thought that the original crannogs may have taken just four months to build. Mr Adrian said: "Unfortunately we do not have the labour. Everyone working on the project is a volunteer, mainly students." In ancient times there would have been a group of eight men working from dawn to dusk.

The temptation to use modern technology would have defeated one of the aims, to discover how the Bronze Age Celts built these structures. No metal bolts or nails have been used. The huge timbers are bound by bracing and lashing.

It is thought that the crannogs were built as a way of defending the communities and their animals from attack. Approachable only by boat, circular for optimum visibility and well above water, the crannogs were easy to defend.

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On display in the visitors' centre will be some of the finds from Loch Tay - many of which raise more questions than they answer. They include a ten-metre dug-out canoe thought to have been used for trading opium seeds and parsley.

This indicates that trade was taking place between these remote highlanders and the continent as early as 2000bc.