Sampietrini are the small stones of black basalt painstakingly laid in all the old areas of Rome and many other Italian cities. It would be impossible to even attempt to calculate how many Sampietrini there are in Italy and how long it took to lay them all.
They can be placed in different patterns to create stylish and distinctive effects.
They are long and wedge-shaped so that they can be tapped securely into place.
Skilled workers lay the stones on sand using plumb-lines and mallets.
It may seem an inefficient way of going about things, but they offer the advantages of leaving small spaces for the water to run off, easily adapting to irregularities, great strength and abiilty to resist quite big movements of the ground.
It is easy to see how they may have evolved from the larger stones used in Roman roads.