I agree, it's the exception

Mannheim comes to mind: http://www.openstreetmap.org/#map=15/49.4877/8.4640

Karlsruhe is listed as an example in the Book, although considerably less regular than most US cities I've been to: http://www.openstreetmap.org/relation/62518#map=15/49.0064/8...

Piacenza has the roman squared city center intact in layout[1], lots of other small towns as well, but the fact is the old town parts are likely too small to actually matter when you look at the whole city layout - hard to notice from just looking at the urban map!

then you have places like Turin that were built with a ruler [2]

https://www.google.it/maps/place/Via+Camillo+Benso+Cavour,+3...

https://www.google.it/maps/place/Turin,+Metropolitan+City+of...

edit: some more samples, with cardo/decumano marked when known

naples https://www.google.it/maps/place/Naples,+Metropolitan+City+o...

parma (barely visible, linked plaza was the old forum) https://www.google.it/maps/place/Piazza+Giuseppe+Garibaldi,+...

verona https://www.google.it/maps/place/Via+Rosa,+7,+37121+Verona+V...

firenze, you can even see the old walls

https://www.google.it/maps/place/Piazza+della+Repubblica,+10...

you are probably right, the old town parts probably get lost in the largest map.

But as far as I know naples is not even a roman city, so I don't know what is going on there :)

my bad, I mixed up generic squared block in cities (turin, naples) with old roman squared blocks arrangements that survived today (the others)

I'm not sure if it has anything to do with Romans, but look at La Valetta, Malta: https://www.google.com/maps/place/Valletta,+Malta/@35.899060...

La Valetta is a planned fortified city built by Francisco Laparelli[0] for the Order of St John in the 16th century.

Nothing to do with the romans, or with normal maltese city architecture (which is much more organic)

[0] https://en.wikipedia.org/wiki/Francesco_Laparelli