Is a Tower Defense type game, but instead of the normal path that the mobs walk a long you must hold them off for certain length of time.

The game is based on the player building a castle that can with stand an assault and keep the king safe. To start off with there would only be simple building materials such as stone and wood. The first few levels the attacks on your castle would be more by smaller raiding parties then proper assaults.

The game would not have the typical tower defense where you are able to build structure while the assault is taking place. Instead you get your resources from the previous defense and must then use them to upgrade your castle during the short break before the next assault. The assaults will only last for set period of time after it has expired any remaining attackers will retreat.

Upgrades to the castle can be adding archers to walls increasing the height of walls, adding murder holes to tunnels and other medieval methods used to repel attackers.

As the levels progress the attackers will get stronger and start to possess siege engines and ladders.

image source: http://appadvice.com/appnn/2012/06/quickadvice-besieged2