 Complete the following phrase:  Persian King Darius I the Great , in an attempt to subdue the Scythian horsemen who roamed across the north of the Black Sea, crossed the Bosporus, then marched towards the River Danube. His army crossed the Bosporus using an enormous bridge made by connecting Achaemenid boats. This bridge essentially connected the farthest geographic tip of Asia to Europe, encompassing at least some 1,000 metres of open water if not more. Years later, Xerxes I would construct a similar boat bridge on the Dardanelles Hellespont strait 480 BC, during his 