Complex sentence: Coes of Mytilene, attended Darius Hystaspes in his Scythian expedition as commander of the Mytilenaeans, and dissuaded the king from breaking up his bridge of boats over the Danube, and so cutting off his own retreat.
Split into simpler sentences: Coes of Mytilene supported King Darius Hystaspes of Persia in his Scythian expedition as commander of the Mytilenaeans. Coes dissuaded the king from breaking up his bridge of boats over the Danube, and so cutting off his own retreat.