What is a top strap on a revolver?

Question

Some revolvers like the earliest Colts do not have top straps, and that is the easy way of telling them apart from the early Remingtons or from any modern revolvers.

What exactly is a top strap on a revolver?

Answer 1

The top strap on a revolver is the part that goes over the top of the cylinder as you can see on this picture of an 1858 Remington.

Image Source

For comparison, here is a picture of a 1851 Navy Colt which doesn't have a top strap.

Image Source

Finally, here is what an assembled 1858 Remington looks like,

Image Source

and here is what an assembled 1851 Navy Colt looks like (notice the lack of top strap).

Image Source

The reason revolvers stopped lacking top straps is because top straps make for a stronger gun.

The Army rejected the pistol and asked for a more powerful caliber with a stronger frame. Mason redesigned the frame to incorporate a topstrap, similar to the Remington revolvers, and placed the rear sight on the rear of the frame; he consulted with Richards on some other improvements.

Source