In the soil surrounding Mount Vesuvius, the "pomodori di San Marzano" — meaning tomatoes of the San Marzano region — prosper along vines in Italy's Sarno River Valley.

The phosphorus-and-potassium-rich earth helps those tomatoes reach their full potential, giving them a sweet, pronounced flavor.

The fruit has a Protected Designation of Origin status, which requires it to be grown in Vesuvian soil. There are many knock-offs, so be sure it has the P.D.O. sticker when buying.

These tomatoes are delicate, red, and sugary in taste. As a result, they are one of the only tomatoes Neapolitan pizza makers consider high-quality enough for their pies.

Neapolitan pizza has a special Designation of Controlled Origin, which defines strict regulations for the pizza. San Marzano tomatoes must be used to qualify as a Neapolitan pizza.

The fact that chefs must use San Marzano tomatoes grown in Vesuvian soil to make genuine Neapolitan pizza is great for Naples' economy, as well.