Which words and phrases show that the passage is a reliable source? Ancient Sparta

Sparta was one of the most influential city-states of ancient Greece. It had the most powerful army in all of Greece. Warfare was the cornerstone of the Spartan economy. Young boys from the age of 7 were sent off to military schools to train. According to a website maintained by the History Department at Oxford University, Sparta’s government was a monarchy ruled by two kings. Leonidas was one of the most influential rulers of Sparta. The British Museum states that Leonidas defeated the Persians with only a small army. A blog maintained by a history student says Leonidas fought the massive Persian armies with merely 300 soldiers.