Venture capitalists are head-over-heels in love with platform markets these days. Most of the so-called unicorns — startups achieving billion-dollar valuations — are platforms: markets that connects buyers, sellers, and others, with the platform standing between them. Uber, Airbnb, WeWork, Amazon — they’re all platforms. Their current vogue might lead you to believe that they’re a 21st-century tech innovation. They’re not. Platform markets have been around for centuries. And as with most things, today’s platform designers may learn something from knowing a bit of this history.