This feature in it is because of presence of a curved headboard and footboard that is outwardly curled at each end’s top. This footboard is often found to be shorter than the headboard. History records suggest when these were used traditionally; it did have a feature imbibed in it because of which it could curl inwards as well as outwards. Those days they were known to be made of wood. The popular practice during this period was to place them in the centre of their rooms. The objective behind this was to highlight it as one of the primary pieces of furniture of that particular room. Generally, people took immense pride in showing their prized possession.
Also be sure to measure the bed frame, if you already have one. This will also need to fit within the headboard. The general rule when measuring the height of the headboard is this: measure half way up the wall of the room where the headboard will be placed against. Your headboard should never exceed this height! Try to find a headboard that either reaches half way or down to a few inches below that point. This will prevent the headboard from "crowding" and overpowering the room.