In the 18th and 19th centuries, mounting blocks were common in cities, towns, and villages. Usually made of stone, they were installed in key locations, usually near inns, churches, country houses, to aid mounting or dismounting a horse, carriage, stagecoach, etc.
The more elabarote mounting blocks are called carriage steps — these slabs had steps carved into the stone.
Together with hitching posts and guard stones, they were important and functional elements of the horse-drawn transportation infrastructure.
My dad was recently in Charleston, SC and took a lot of photos of carriage steps for me: