Here is a prediction on how the Charrs bring down Ascalon in 1090AE.
Ascalonians held their ground against a much superior Charr army since 1072AE. They did this by holding on to 4 strategy locations on the Great Wall. They were:
2) The Breach
3) Great Northern Wall
4) Eastern Wall
King Adelbern decided long ago that neither of the 4 positions can fall. An open field battle against the much superior Charr army is hopeless. And hence all available Ascalon troops were sent to one of the 4 positions to maximize their manpower. Actual men left behind to defend the capital city was limited. This doesn't matter though, since the capital city is safe as long as those 4 positions remains in Ascalon hands.
And for years the plan worked. The Charrs does occasionally "nearly" break though the positions. However troops were able to relocate and drive back the Charrs.
To understand Ascalon's sudden fall in 1090AE one must understand the Catacombs under Ascalon. Here is a map of pre-searing Ascalon, when the Catacombs were still wildly used.
The Catacombs connects various places in Ascalon together. In Pre-Searing travelers would often use the Catacombs. However after the Searing the Catacombs were abandoned. It was rarely mentioned and by 1090AE it was mostly forgotten.
However Charr captured a historian that remembers the Catacombs, and thought torture was able to force him to reveal the enterance locations. There were 2 key exits. Barradin Estate and Ashford Abbey (currently Sardelac Sanitarium). The Barradin Estate exit was only a few miles south of The Breach, while the Ashford Abbey exit was only a few miles south west of Ascalon City itself. Getting troops to Ashford Abbey would allow the Charrs to avoid the Ascalonian defenses and attack their capital city directly. A plan was drafted and carried out.
The Charrs did a major attack against The Breach while another legion matched on to the Barradin Estate exit. As expected, the Catacombs were mostly forgotten and the Charrs got to the weakly defended exit with ease. The Ascalonians didn't sense the seriousness of the situation, and focused on defending The Breach. From there they got to Ashford Abbey and then match onward to the weakly defended Ascalon City.
By the time King Adelbern realized what was going on hundreds of thousands of Charrs has already surrounded Ascalon City. He ordered troops from the 4 defensive locations to rush back to Ascalon City for defense. The forces in the Great Northern Wall were the closest and the first to made it back. With their help King Adelbern was able to defend the city for a few days.
However doom is near. The troops from the other 3 positions never made it back in time to help. And the 4 defensive positions were weakened, and they fall one by one. The Great Northern Wall was no exception. After it falls the Charrs were able to attack Ascalon City from both the South-west and the North. The battle became hopeless.
King Adelbern was furious for being outsmarted by the "barbaric" Charrs. He ordered all surviving Ascalonians to abandon post and escape to Ebonhawke. He then casted Foefire. Millions of lives, both Charrs and Ascalonians, were lost. The rest was history.