Greek colonies settled the Sicilian and Southern Italian coasts well before the Romans
The Greeks settled Sicily and southern Italy centuries before the Romans expanded south, so their art celebrating the perfection of proportion, balance, harmony, and form is part of Italy's heritage.
Where to find Greek art in Italy
The world's best surviving ancient Greek murals are in Paestum's museum, including the famed Tomb of the Diver frescoes.
There is also some fine sculpture in the archaeological museums of Siracusa and Palermo (in Sicily), and Taranto (in Apulia), as well as numerous Roman copies of Greek originals filling just about every Italian archaeology museum from Milan to Rome to Siracusa.