Marinara is not a synonym for tomato sauce. Real marinara sauce has the taste and juice of fresh tomato, but also a velvety texture and the rich bite of olive oil. The trick to perfect marinara is to cook it at a vigorous simmer, so that the tomatoes are cooked through just as the sauce becomes thick. The tomato pieces hold their shape and the color stays bright red. Done right, it explains why spaghetti with tomato sauce is a dish that a person might crave virtually every day.
Italian-American cooks treated it as a multi-functional ingredient: a starting point for other sauces, the base of a soup, the acid that breaks down meat in a stew. And now, to the tomatoes. If you happen to live near Mount Vesuvius, by all means use ripe local tomatoes. Some canned tomatoes from the area around Naples, characterized by volcanic soil, plentiful sunshine and salty breezes, are certified by the European Union as “San Marzano” tomatoes. San Marzano is a Denominazione d’Origine Protetta, meaning that the tomatoes are grown, processed and packed there.\
Read all this and more at the NY Times