Earlier (pre-1600 CE) depictions of bridles show little or no detail of how such equipment was attached or adjusted, and the scanty archaeological evidence tends to support that idea that it was not just because the artists did not judge such detail to be relevant. The reason is quite straight forward. In pre-modern times such tack was not mass produced and bought off the peg to applied to a random horse, or swapped between mounts as today. They were generally bespoke pieces made to be a reasonable fit to a particular animal, and so did not need the degree of adjustability expected today. Another aspect is the fact that in earlier times, the bit was normally fixed to the bridle. A challenge has been to create bridles which look like those earlier styes, but nevertheless allow for some degree of adjustment as expected nowadays, and to allow owners to attach their preferred bridle themselves.
From 1600 onwards, while bespoke items continued to exist, bridle forms rapidly attained familiar modern styles.
Aside from the fixed versus adjustable distinction, because horses have not fundamentally changed shape over time, nor has what a bridle needs to do altered, some styles of bridle recur over long periods of time.
Copyright: Timothy George Dawson 2021