Endless

With the work held as at left strike the fattest part a blow, shift it along its length in the direction you want it to get thinner and strike it again a little more gently, continue doing that until you get to the end, then if you still have a fairly soft red color rotate it 90 degrees and do the same on the neighboring face. Here I would be pulling the bar toward the left and gradually reducing the strength of blows with each shift.

The lower picture shows a bar that has only had a couple of blows applied on two faces. Holding the bar flat on the vice you can work out all the divots to give a smooth sided taper.

The shape the bar makes when struck on a more square shouldered anvil edge reminds me of the Brancussi sculpture, which I believe is called Endless column. I don't suppose he was into smithery, but it does seem appropriate that similar forms to his endless module are to be found in metal being drawn out into infinity.