The Mexican cuisine of today originated thousands of years ago. The ancient Olmec and Mayan civilizations domesticated maize, beans, and chili peppers and developed the flatbread cakes known as tortillas. The Aztecs expanded the Mexican diet with other meats, fruits, and vegetables. As Spanish explorers conquered and colonized Mexico, European cooks introduced new ingredients, such as rice, wheat flour, and the meat of domestic animals like pigs, chickens, and cows. They also brought previously unknown methods of preparing food, such as frying. Today, Mexican cuisine is extremely popular far beyond the borders of the nation, and in 2010, the United Nations Educational, Scientific and Cultural Organization (UNESCO) declared Mexican cuisine to be an "Intangible Cultural Heritage of Humanity."