What can I do with my gold

Hint 1 of 5:

You can hire foot soldiers.

Hint 2 of 5:

Or you can hire knights.

Hint 3 of 5:

Catapults could be useful if you like raiding castles.

Hint 4 of 5:

Most important of all,

Hint 5 of 5:

You need to build castles to protect yourself from invaders.