Ancient Americans were cultivating many chillies 1,500 years ago, indicating that the spicy, hot cuisine of modern Mexico has a long history.
Ancient Americans liked their food hot - as do many Mexicans today
US archaeologists examining soil layers found that inhabitants of Mexican cave settlements grew and stored at least 10 different kinds of chilli peppers.
They also found that fresh and dried peppers were used by ancient peoples.
"You don't grow different chillies unless you're cooking interesting food," one of the archaeologists said.
Researchers Linda Perry and Kent Flannery excavated areas in Guila Naquitz and Silvia's Cave near Mitla in the southern Mexican state of Oaxaca.
Their findings were published in the Proceedings of the National Academy of Sciences.
They discovered 10 cultivars of chillies in layers of earth dating between 500 and 1,500 years.
"What was interesting to me is that we were able to determine that they were using the peppers both dried and fresh," Ms Perry said.
"It shows that ancient Mexican food was very much like today."
The remains of food were found in caves used as temporary camps and storage areas by Zapotec-speaking peoples, their study said.
The cave deposits indicated that the peoples had a sophisticated agriculture and cuisine.
The site at Guila Naquitz has plant remains dating back 10,000 years, pointing to the cultivation over many centuries of corn, beans, avocados and squash as well as chillies.
In an earlier study, the same researchers found evidence that chillies were used in cooking in Ecuador some 6,000 years.