 Bulfinch's design, with an operating amphitheater under the dome, was probably based on that in the Pennsylvania Hospital building, which he probably saw on a visit in 1816.That amphitheater, now known as the Ether Dome, is where the first public demonstration of the use of ether as an anesthetic took place on October 16, 1846.The amphitheater was designated a National Historic Landmark in 1965 in recognition of this event.