I have been trying to find a cut off point for when the definition of a crown included arches. There are numerous examples of crowns without arches. On this board e.g. The Crown of Princess Blanch is a good example Reading Boffer's post at the top of this post it's clear that the 1917 letters patent clarify the situation. But when was it first agreed that a crown should have arches? I may be snowed in over the next few days so there may be time for further research.