Short answers, pulled from the story.
Magna Graecia was the historical Greek-speaking area of southern Italy, encompassing the modern regions of Calabria, Apulia, Basilicata, Campania, and Sicily. Greeks began settling the region extensively in the 8th century BC, founding independent city-states that became centers of Greek civilization outside the motherland.
Sybaris, now Sibari in Calabria, was the most populous city in Magna Graecia, with an estimated population of between 300,000 and 500,000 from 600 to 510 BC. It was destroyed around 510 BC by the forces of Kroton, commanded by the athlete Milo of Croton.
The first Greek city absorbed into the Roman Republic was Neapolis in 327 BC. Most of the remaining cities were annexed in 205 BC, following the Second Punic War, as punishment for siding with Carthage.
Magna Graecia produced Parmenides and Zeno of Elea, Gorgias of Lentini, Empedocles of Agrigento, the mathematician Archimedes of Syracuse, and the doctors Alcmeon and Democedes of Crotone, among many others. Pythagoras founded his school at Crotone in 530 BC, and Aeschylus died at Gela in Sicily in 456 BC.
Griko is a living dialect of Greek spoken in parts of Calabria and Salento in southern Italy. Linguists consider it a descendant of Byzantine Greek, blending ancient Doric and local romance elements, and some scholars trace its origins directly to the colonies of Magna Graecia. The Italian parliament formally recognizes its speakers as an ethnolinguistic minority.
The Valle dei Templi at Agrigento, designated a UNESCO World Heritage Site in 1997, is the largest archaeological park in Europe and the Mediterranean basin at 1,300 hectares. Syracuse and its Necropolis of Pantalica, along with the ancient Greek towns of Poseidonia and Elea within the Cilento national park, are also UNESCO-listed sites connected to Magna Graecia.