You can make a straight barrel arch and scale one end to get the taper. If instead you have exact arcs already that you wish to use for beginning and end, you could skin between them with Sandbox, but you'll get better geometry with Curviloft plugin-- skin contours. Depends on what you need. If you have to show thickening, as if it is actually made of bricks, probably the best plugin for that is joint push-pull. If it tapers, I don't see how follow-me could work. If you want, upload a picture here.