Modern Milan, located at the center of a number of important Italian settlements, in the far north of Italy near the Swiss alps, bears little resemblance to its founding. Its principal body of water, the River Po, the longest river in Italy, flows west-to-east. It connected the early settlements through which it flows and has historically been subject to flooding, now contained by man-made dikes. It begins as a mountain spring and ends at a huge delta of the Adriatic Sea near Venice. Its channels near Milan were designed by Leonardo da Vinci. The entire Po Valley was called Cisalpine Gaul in ancient times. The coins of this region begin with a gold solidus of the 5th century and encompass a long, complicated history of money issued by kings, dukes and a number of invaders.