Cobblestones

Since I wrote this, some interesting discussion of the subject at TripAdvisor. See
https://www.tripadvisor.com.au/ShowTopic-g187791-i22-k12084620-Cobblestones-Rome_Lazio.html

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There is a trench being dug, a service pipe of some kind being upgraded, under the cobblestone street, Via Baccina, below our window. Photos below reveal what's under the cobblestone surface.

The mesmerising patterns of cobblestone are an art; artisans make cobblestone roads. The strength of such roads is significant. When you see them uprooted by roadwork you realise how big the individual cobblestones are. 

Given their tapered shape, downward force of traffic increases the upward force effect of the underlying road bed on the cobblestones and the load. They carry immense loads of traffic in some places. They are durable but the way they are made means that there will inevitably be unevenness over time. Cobblestones have a beauty, one of the defining beauties of Rome. As is the sound of tyres on them. And these days the sound of trundled suitcases.

you see the limited space for excavation.

an enlargement from the previous photo, to show the shape and depth of the cobblestones