Once upon a time, some people on a road were stopped by a wall.
We didn’t mind. It was a good place to stop for a while, and as more people coming down the road stopped at the wall, a community grew at its foot. Most people enjoyed gathering together, so the wall seemed like a fortuitous event, a good reason to rest and celebrate and work together for a while.
The wall wasn’t impassable, of course. Some could still clamber over the pile and continue on their journey, but the wall was a little daunting, and the happy community was so tempting, and few bothered.