An army is a group of armed and equipped men joined together to fight a war on land. In an army, the soldiers are organized under the leadership of officers and commanders. The first armies were nothing more than all the men of a tribe fighting together under their chief. Then special men came to be chosen to be the soldiers in a nation. The first really organized armies were those in Egypt, more than 3,500 years ago. The early Egyptian armies were composed entirely of foot soldiers. These soldiers carried spears and bows and arrows.

Not many years later the Assyrian and Babylonian armies had not only foot soldiers, but soldiers in horse-drawn chariots. The early Greek city-states had armies that were well organized. Perhaps the greatest army of early times was led by Alexander the Great, about whom there is a separate article. His army conquered most of the civilized world of that time. The Romans, not long after the time of Alexander, had the bestorganized of all ancient armies. The men were well-trained and led by excellent officers. The Roman armies were composed of smaller groups called legions.

A legion was much like an army division today. The Roman legions were practically unbeatable. They were often outnumbered, but their training and organization were able to overcome the larger groups of the enemy. The Romans had the first army engineers, who built roads and bridges. The Romans also had the best organization for supplying food and equipment to their armies. The Roman Empire finally grew weak and fell to the barbarians. The civilized world was plunged into the Dark Ages, and the art of military organization was forgotten for centuries. During those centuries, armies were mostly groups of peasants led by mounted knights. These armies had very little organization, and were often made up of soldiers who would fight for anyone who would pay them. They usually spent more time in robbing the people than in fighting a battle.