Ettore Roesler Franz was a 19th century German/italian painter, noted in particular for his watercolors of Rome.
A number of these comprise a series titled “Roma sparita” (loosely: “Vanished Rome”), meant in part to record scenes of buildings and landmarks the he feared would be demolished in an effort to modernize the city.
His watercolors are wonderfully textural, with dramatic value contrasts and great use of perspective.
Frustratingly, examples of his work online are scattered and frequently smaller than one might hope. Wikimedia Commons has quite a few, but most are small (though there is a nice larger version of the image above, top here). You can find larger images with a Google search of Sothebys or Bonhams auction sites (below).
The best single source I’ve found otherwise is ettoreroeslerfranz.com, which has a better selection of images at a larger size than Wikimedia Commons. Unfortunately, the site is poorly organized (image sections are linked on the left), and the site plays music at you, and I can’t find a way to turn it off — so use at your own risk of annoyance.