Europeans traded beads, metal bells, horses, pigs, and a variety of fruits and vegetables with Southeastern Indians, and beads and bells were the first items traded here when Hernando de Soto offered glass beads and metal bells to tribal leaders during his expedition. Indians often responded with gifts of fish, maize, or animal skins, but despite these polite exchanges they remained wary of the Spaniards. Bells found in the southern United States are considered evidence of Indian trade with European expeditions such as de Soto's. Spanish explorers brought America's first horses in the 1500s, and when Indians saw men on horseback, they thought the man and horse were one creature. Trade changed Indian life, but the greatest impact came from European diseases, to which Indians had no resistance, and entire villages perished after exposure. Food also crossed continents: avocados, beans, cocoa, corn, peanuts, potatoes, squash, and tomatoes went to the Old World, while apples, broccoli, coffee, lemons, lettuce, olives, peaches, and wheat came to the Americas. Pigs were unknown in America before de Soto arrived with hundreds of swine intended for food and trade, and Southeastern Indians smoked pork over a raised grill the Spaniards called a barbacoa, from which the term barbecue is derived. After two years searching the Southeast's swamps and forests for gold, de Soto reached the Mississippi River in 1541, and he and his 650 men became the first documented non-Native people to see and cross it. A Spanish silver medallion found at the Ingomar Mounds site in New Albany, Mississippi, suggests a visit by Spanish explorers, though it is not known for sure whether de Soto's expedition visited that site.