Evil Grounds

Flying cannon balls, dark growling from the dragons’ necks, war echoes of dangerous giants, these all things can be heard all the time and won’t fade away until the last hell creature dies.

Your fortress has its front wall separated into four parts. On every piece there can be put one cannon. You begin with only one and by shooting the enemies you stop them reaching your wall. If they get close enough they will start destroying the stone safety. When you win, don’t forget to buy other cannon or upgrade the old ones.
The worst problem is among the flying green skulls which quickly move and hitting them is very difficult. The dragons can spit fire so destroy them too.