This battle is based off of a city in my book series, entitled, The Tome of Eldanor (I haven't finished it yet, so don't go looking for it in a book store/library). The town of Lelling is the foremost harbor-town of the world of Eldanor, and it would provide the leader of the Evils, Thayne, the perfect vantage point for the upcoming assault on Oras Tar if he were to capture the city.
The map gives the attackers an army after 17 minutes, so, for that period, the attackers cannot build units, and the defender should not attack. Once the attackers destroy one of the two gates to the fortress (not the ones on the river), they get further reinforcements inside Lelling (trolls, corsairs, and haradrim cavalry). After 27 minutes, the defender is given reinforcements.