The bridge itself was built during the long and prosperous rule of King Alfred II. With no fords on the rivers for miles, it cut the transit time of supply trains from the fertile plains to the lands beyond in half.
The castle was built originally as a massive barracks for defenders of the bridge. Minor incursions, though, caused Alfred to begin a period of expansion in which the large rear segment of the castle was added with a newer, larger keep than stood before.
This map shows the castle as it was shortly before the death of Alfred II. After that time, the kingdom was thrown into disarray when the middle son Michael ascended the throne ahead of the rightful heir Mark. At the end of these conflicts, the castle had been destroyed back to odd segments of crumbling wall, and the bridge had been destroyed.
The setup was simple, but above average - although, as more designers are now adding plots to their maps, this sort of storyline is on the verge of becoming the new average.
Since the storyline didn't say which side to play, I played both. As the ATTACKER, it was very easy to win. 10% losses and the Castle was mine. As the DEFENDER, I lost a lot more troops, but my Lord was never in serious danger.
This is another map where you get fired upon as you enter the game... =(