Okay kiddo, so back in the olden days in a place called Byzantium (which is now Istanbul), there was an army that was very important. This army was called the Byzantine army.
The Byzantine army was very strong because they had a lot of soldiers who were very good at fighting. They had soldiers called cavalry who rode horses and soldiers called foot soldiers who walked on the ground. The horses were big and strong, and the foot soldiers carried weapons like swords and spears.
The Byzantine army was also smart. They had clever ways of fighting that helped them win battles. For example, they would use a formation called a phalanx, where the soldiers would stand closely together to protect themselves from the enemy. They would also use a thing called a catapult to throw big rocks at the enemy from far away.
The Byzantine army also had leaders who were very good at making plans. These leaders were called generals. The generals would tell the soldiers what to do and where to go during battles.
The Byzantine army was very important because they protected the Byzantine Empire, which was a big part of the world at that time. The army fought against enemies who wanted to take over the empire, and they protected the people who lived there.
So there you have it, the Byzantine army was a group of strong soldiers who were very smart and protected their kingdom.