Your Capital is the heart of your Empire. If your capital is taken over, it is instantly game over for you, which makes it crucial to keep checking on it and make sure no other empires are making their way towards it. The most common way an empire falls, is when a Tower is used to capture it. This is mostly because a tower can claim 4 hexagons in a straight line and it can be hard to notice a tower 4 tiles into the enemy's territory being set up. It can be said that using a tower to take someones capital and cause their empire to fall is cheap, but it still to tends be much less stressful for most then having their capital claimed by normal means. Sometimes your capital may be almost completely surrounded by Water, which is very useful if there is only one tile that can be claimed next to your capital.