Usually served as past'ascuitta with a sauce, although sometimes in soup. Usually square, though they can be round too. Ravioli go back at least to the Middle Ages (recent research in fact suggests they were invented in 6th-century Persia, in the court of the famously gourmet Sassanid ruler, Khosrow Anushirvan). They even appear in 14th-century English writings on cookery, as 'tartelettes', apparently derived from tortello.
There are variants with different names around Italy: agnolotti (Piedmont) tortelli or tordelli (Lombardy, Emilia-Romagna, Tuscany), cjalsons (Friuli, Venezia) and culurzones or culingionis in Sardinia, a name that recalls the original Persian, khushknanaj.
Ravioli can be stuffed with meat, cheese, mushrooms, or just about anything—including potato, seafood, pumpkin and apples. Spinach and ricotta are perhaps the most common filling. Large ones can be called ravioloni.
ravioli capresi: from Capri, stuffed with local cheeses and marjoram.
ravioli dolci: 'sweet ravioli' are made around Italy, especially at local festival times; they're a speciality of the Abruzzo, with a stuffing of ricotta, sugar, cinnamon and lemon.
ravioli alle erbe or alle erbette: with greens (especially wild greens) and cheese.
raviolo ligure, or alla genovese: meat, borage and marjoram, or greens and cheese.
ravioli di magro: spinach ricotta and parmigiano.
ravioli alla milanese: beef, prosciutto and cinnamon.
ravioli con radicchio rosso (di Verona): stuffed with chopped radicchio, prosciutto and cheese.
ravioli di San Pancrazio: another sweet ravioli filled with ricotta, made around Montefiascone in north Lazio for the saint's festival in May.
ravioli scapolesi: big ones with meat, sausage, beet, potato, cheese, cumin and fennel (Molise).
ravioli al vapore: steamed Chinese jiaozi dumplings.