In a couple medieval-ish fantasy novels I've read lately (WoT, ASOIAF), gravel is mentioned as a groundcover in castle courtyards. As far as I know, gravel is really, really labor intensive, even with modern machinery. Is this an accidental anachronism, or was gravel common before modern machines? How was it made?
Gravel can be mined from gravel pits, as well as from the bottom of streams and rivers. Most gravel with rounded stones is mined from ancient riverbeds. As such, given that medieval industry would have included mining for tin, iron, copper, gold, lead, slate, silver, and quarries for granite, limestone, sandstone etc, they would also have had quarries for gravel and sand, pretty much as we do today.