I wonder sometimes how Orthodox life in Frankfurt might have been different had the Chasom Sofer not left to follow his rebbe Noson Adler. R' Adler had been driven from town due to his kabbalistic interests.
The Chosom Sofer wound up in Pressburg, which is 40 miles from Vienna. In the book Pressburg Under Siege he describes the assault of Napoleon's army on the city. The book is a rare glimpse into life in Pressburg at that time and a narrative by a gaon of life in his city.