Filled Lecture Hall in the Smithsonian Institution Building, by Unknown, 1857, Smithsonian Archives - History Div, Engraving of the Lecture Hall in the Upper Main Hall of the Smithsonian Institution Building, or "Castle" shows an audience listening to a lecturer with demonstration using scientific apparatus. The engraving was published in the Smithsonian Guidebook of 1857. Pew-like bench seats held over 1,500 attendees. The Hall was used from 1855-1865 until the fire of 1865 destroyed all the upper rooms of the building. The lecture room was used for scientific demonstrations, free public lectures, meetings and concerts. The design of the room afforded clear sight-lines and evidently superb acoustics. There is both a lower area and a balcony area..