[ovi256]

Depending on the country, you can find many public domain maps, scanned, in the Library of Congress.

Here's the famous 18th century Cassini map of France (first modern triangulated map, three generations of Cassinis worked on it)

https://www.loc.gov/item/gm72002942/

The LoC graciously scanned and hosts this copy. Arcanum also sells it: https://maps.arcanum.com/en/map/europe-18century-firstsurvey...

You'll notice that the Arcanum map is scanned, tiled, and hosted as a modern web scrollable map.

[Bayart]

The Cassini map is available in a scrollable format from the French government itself : https://www.geoportail.gouv.fr/donnees/carte-de-cassini

Furthermore the site hosts a number of historical and modern maps that are all geographically indexed and can be overlaid.