Over the centuries, the Greek islands have been the stepping stones between North Africa, Asia Minor and Europe, across which warriors, tradesmen, conquerors and even civilisations have hopped. Since ancient times the islands have been fought over and claimed as prizes by successive invaders. Their strategic location, in a seafaring world, made many islands prosperous and autonomous trading centres. Some were run by foreign masters, as evidenced by the Venetian ports, Roman aqueducts and Frankish castles found on the islands today.