From the Tsu. website:
"No one knows exactly when the idea for roller chain was first conceived, although the brilliant 15th century inventor Leonardo da Vinci produced a series of sketches illustrating basic roller chain. Some of these drawings closely resemble the actual form of modern day roller chain. However, it wasn't until the late 19th century, when it was adopted for use in the drive mechanism of bicycles, that roller chain was manufactured on a large scale. And now, despite the fact that it has been in widespread use for more than one hundred years, the basic form of roller chain has changed very little -- a magnificent testimony to the effectiveness of its original design."
http://tsubakimoto.com/products/chain/index.html