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stone age people wanted safer ways to cross bridges and without getting wet, they began placing a pile of rocks in the centre of a river, where the first beams were made and then they would lay a slab of stone to the pile of stones and another piece from the supports of opposite sides.
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the wood did not last long so stones were the placed in replace of logs.
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a plank placed between a stepping stones. logs tied together formed wider decks or pathways to cross over.
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trees had fallen naturally over streams and rivers and helped people get across