Why use basalt?
A Roman road paved in basalt
(This is from Trajan's Market in Rome)
Egyptian basalt statue
of Cleopatra (not that Cleopatra,
but an earlier one, related to her)
from the Hermitage Museum in Russia
Basalt is a very hard, black stone, and so the Romans used it for roads, because it would last a long time. People in the ancient world also used basalt for grinding stones, to grind wheat and barley. Roman traders often shipped basalt (bu-SALT) grinding stones on sailing ships to markets all over the Mediterranean, so people could have good grinding stones even where there weren't any volcanoes.
A basalt grain mill from
the Roman town of Ostia
Volcanoes, by Peter Francis and Clive Oppenheimer (second edition 2004).