They were feared as the greatest, and bravest, sailors of their age. Now the mystery of how Viking warriors and tradesmen navigated their way across the high seas centuries before the first compasses reached Europe may have been solved.

Scientists today said the Norsemen used special crystals called 'sunstones' to reveal the location of the sun even when it was hidden by fog and cloud. The crystals, which are common in Scandinavia, detect the way sunlight is scattered when it hits the Earth's atmosphere.

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