"High ground is easier to defend as it provides an advantage in both defense and offense. From a defensive standpoint: you're able to see your enemy approach from distance, you can perform overhead attacks easier with with help of gravity"
"Fighting from an elevated position is said to be easier for a number of tactical reasons. Holding the high ground offers an elevated vantage point with a wide field of view, enabling surveillance of the surrounding landscape, in contrast to valleys which offer a limited field of view."
"Being up on the high ground gives you more choice of when you drop to engage an enemy, giving you control over the fight, and a natural advantage. Another way high ground gives you a better angle to fight."