This is one of the rescued scenarios from Stronghold Central. Original readme as follows:
Map Name: Rat Trap
Map Type: Stand-Alone Invasion
Designer: Calreph (Steve Perkins)
Date Complete: 12/02/2001
Filename: Rat Trap.map
E-mail: firstname.lastname@example.org (for comments, suggestions and criticism)
Standard invasion map.
In this scenario, you will have to complete a partially built stronghold abandoned by the Rat.
Get your economy running and prepare your defenses.
The Rat will attack in roughly eight years with a quick succession of invasions consisting of about 1000 troops.
You are provided with initial supplies of various weapons but will need to manufacture many more to be victorious.
The only trade option is wood.
Stone, iron and pitch resources are available.
I've tested the scenario four times on difficulty level Hard.
The entire siege normally lasts about three years.