The Romans had flush toilets and central heating, and they used concrete in their buildings. Nitrous oxide was discovered in 1772, though nobody figured out that it worked as an anesthetic (as opposed to a recreational drug!) until 1844. And Antonie van Leeuwenhoek invented a microscope good enough to see individual cells in the 1660s.
Most people — most of the rather odd people I hang around with, at any rate — keep a few of these seemingly anachronistically early uses of technologies in their mental factoid warehouse. These bits help us explain unexpected relics, like the Roman aqueducts and buildings (like the Pantheon) that are still standing after well over a millennium and a half.
Photo by Marco Arment.