Below the square the rats run in the darkness of the sewers, one behind the other's tail, along with conspirators and smugglers: they peep out of manholes and drainpipes, they slip through double bottoms and ditches, from one hiding place to another they drag crusts of cheese, contraband goods, kegs of gunpowder, crossing the city's compactness pierced by the spokes of underground passages.

This is from Italo Calvino's "Trading Cities 5" (chapter 6, p.88), a short story taken out of Invisible Cities.