.The tendency for a front arch is to spread, but with a rear arch the tendency is to sink under the weight of the rider. Like the front arch, it must be high enough to clear the spine, but the question of width is by no means so important as in the front arch, while the strength of material is equally important.

The side bars
The side bars are that portion of the saddle which rests on the back, and to which the front and rear arches are secured.Side bars are generally made of wood, and are given a twist in the making which enables them to be adjusted to the curves of the back.

Materials for side bars
Side bars may be made of metal, but these are not in common use; wood, be it either for a military or plain saddle, is the substance generally employed. If the shape of the vertical section of the body beneath the front and rear arches, be looked at, it will be obvious that the shape of bar suitable for one is unsuitable for the other, and speaking broadly we may say that while the side bar in front tends to be upright, behind it tends to be flat. This difference in shape is accomplished by giving the bar a twist in the process of manufacture.

We have dwelt on the fact that all horses do not have the same shape of back, yet most side bars are so alike that one cannot be distinguished from another.

Use of side bar
The function of a side bar is to afford a firm support for the arches of the saddle and to distribute the weight over the back.
Bearing in mind the weight bearing region, viz., from the play of the shoulder to the rib, it is clear that over this surface the side bars should rest evenly, squarely, and without undue pressure at any one point. Such is the theory; the practice, however, is very different, arising from difficulties which are not always capable of control, especially the exigencies of military life.