The curb bit, though used in the time of the Roman emperors (in an ancient sculpture Theodosius is represented riding with one of extraordinary leverage), was not adopted by the English until Charles I. in the third year of his reign issued a proclamation, commanding that no person serving in the cavalry should use the snaffle, but in lieu thereof the curb only.
On the frieze of the Temple of Minerva, in the Acropolis of Athens, the horses are represented as ridden (as in the races through the Strada Reale in Malta they are still ridden) without bridles or saddles.
The best bridle for a horse is, of course, that which is best adapted to the particular work he is required to perform.
For racing over turf, where he is required to extend himself like a greyhound, the snaffle-bit only is almost invariably selected.
For cavalry purposes, where he is required suddenly to throw himself on his haunches, wheel to either side, or right about, the curb-bit is added; while by the Turks and those Asiatics who practise their horses to approach a wall at full speed, stop, turn round, and then gallop back again, a curb-bit only is used.
For hunting, both bits are necessary; for while across turf, light soil, and over fences of almost every description, the snaffle is a safer guide than the curb-bit, yet in going through deep ground the latter is absolutely necessary to enable the rider, by holding his horse together, not only to prevent him from extending himself—in which attitude his hind feet would overreach his fore ones before they could be extricated from the sub-soil—but to stop him quickly, for instance to pop through a gap on either side, which he would otherwise override for a considerable distance.
To leap over the hedge of a plantation full of trees on a hot horse, with only a snaffle-bit in his mouth, would be dangerous, and often impracticable; whereas it might easily be effected with a curb-bit, by which the animal could moreover be made to ascend a steep narrow bank, creep along it, and then jump off it, over perhaps the only practicable point in the fence beyond it.
The shape, make, and leverage of bits of all descriptions of course depend on the mouth and disposition of the particular animal for which they are required.
It may, however, be generally stated that for all horses a plain snaffle is better than a twisted one; and that of curb-bits, those are the best which give to the rider the maximum of mechanical power, with, to the noble animal beneath him, the minimum of pain.