The Assembly Rooms were designed in 1769 to host the great balls of the English Aristocracy, they formed the hub of fashionable georgian society. Bath was most alive during the social season when Mothers and Chaperones would bring their daughters to meet a suitable husband.
Bath is the social center for most of Jane Austen's novels, and Northanger Abbey and Persuasion are both set in Bath. Most of her novels either mention the parties in the Assembly rooms or have scenes in the ball rooms themselves.
Now, the rooms are open for private functions and can be toured during the day. The lower levels of the building house the Fashion Museum. The museum shows the high society fashions from the 16th century to present day.