 Although the upper part of the frame only supports the beam's central pivot and any Watt's parallel motion gear, it also has an important function in stiffening the frame overall against vertical bending forces between the cylinder and crankshaft.Cast iron is weak against bending, and a shallow frame alone would need either rigid masonry support, or would soon fracture.One of the oldest surviving six-column engines is a small engine of 1820, possibly by Boulton & Watt, preserved at the Birmingham Museum of Science and Industry.