During the Mughal reign, successive emperors built forts afresh or modified existing forts/similar structures to suit their needs. The sprawling Agra Fort is said to have been built by modifying a fort called Badalgarh, constructed by a Rajput chieftain. Read more interesting facts at http://www.agrafort.gov.in/story_af.html
The Diwan-E-Aam was the place demarcated for the Emperor to hold audience with his subjects. Such ‘Halls of Public Audience’ are found in the Agra Fort, Fatehpur Sikri, Lahore Fort and Red Fort etc. The halls are large, pillared structures with remarkable acoustics – even whispers are amplified at certain spots.
A dangerous place to gossip indeed!