Of Alexander's army of thirty-five thousand, thirty thousand were foot soldiers, and about five thousand were horse. More than half the whole army was from Macedon. The remainder was from the southern states of Greece. A large body of the horse was from Thessaly, which, as will be seen on the map,[A] was a country south of Macedon. It was, in fact, one broad expanded valley, with mountains all around. Torrents descended from these mountains, forming streams which flowed in currents more and more deep and slow as they descended into the plains, and combining at last into one central river, which flowed to the eastward, and escaped from the environage of mountains through a most celebrated dell called the Vale of Tempe. On the north of this valley is Olympus, and on the south the two twin mountains Pelion and Ossa. There was an ancient story of a war in Thessaly between the giants who were imagined to have lived there in very early days, and the gods. The giants piled Pelion upon Ossa to enable them to get up to heaven in their assault upon their celestial enemies. The fable has led to a proverb which prevails in every language in Europe, by which all extravagant and unheard-of exertions to accomplish an end is said to be a piling of Pelion upon Ossa.