Pesto is an Italian sauce that originates in the Liguria region of Northern Italy, specifically in the city of Genoa (pesto alla genovese), although at least one other well-known variant exists: pesto alla siciliana, a sauce from Sicily that replaces the basil of Genovese pesto with tomato. Pesto has been known, in various forms, since Roman times, and probably was imported from North Africa. Pesto, usually sold in small jars, is commonly available in stores in green (original) or red (with sun-dried tomatoes or red bell peppers) varieties, produced by major manufacturers or under a 'generic' brand. Pesto alla genovese is an European protected designation of origin (PDO) food , that means that, to be allowed to use this name, producers have to use the traditional ingredients: basil, garlic, salt, pine nuts, extra virgin olive oil, Parmigiano Reggiano cow cheese and (optionally) pecorino sardo sheep cheese. In commercial lower quality pesto, cashew nuts or walnuts are often used instead of pine nuts, as they are cheaper and have a similar texture. In addition, the Parmigiano is often replaced by cheaper varieties of cheese, such as Grana Padano or Parmesan cheese and cheaper oils are used. It is commonly used on pasta, soups, crackers, and bread, though its use is not restricted to these as the sauce is highly versatile.