What is the main ingredient in a traditional pesto sauce?

The main ingredient in a traditional pesto sauce is basil. This herb is the cornerstone of the classic recipe, which originates from the Liguria region of Italy. The traditional preparation combines fresh basil leaves with pine nuts, garlic, Parmesan cheese, and olive oil, creating a vibrant and aromatic sauce that's commonly used with pasta, as a spread, or in various Mediterranean dishes. The characteristic flavor of pesto is largely due to the freshness and unique taste of basil, making it essential to the sauce's identity. Other herbs like mint, cilantro, or oregano may be used in different variations of sauces, but they do not define the traditional pesto that is widely recognized and cherished.