El Camino Real de Tierra Adentro, or the Royal Road of the Interior, was the most important trading route in the American Southwest for more than 300 years. Don Juan de Onate, the last Spanish conquistador, blazed the road in 1598, creating the first highway in what today is the United States. He connected Mexico City to the lands that would become New Mexico, following Native American trading paths the Piro people established centuries before along the Rio Grande. As he journeyed north into New Mexico, Onate opened the territory for colonization, and established San Juan Pueblo, the first Spanish settlement in the territory, at the end of El Camino Real.

Stretching for more than 1,500 miles, the road brought Native and Spanish cultures together, creating the Southwest's unique blend of food, architecture and religion. After Mexico declared independence from Spain in 1821, the newly opened Santa Fe Trail linked to El Camino Real, bringing Anglo-Americans into the Southwest. Although the arrival of the railroad in the 1880s caused traffic on El Camino Real to rapidly decline, wagon ruts are still visible more than a century later.

Today, Interstate 25 roughly follows the old road. The U.S. Congress declared El Camino Real a National Historic Trail in 2000, and museums and historic churches await visitors along the route. El Camino Real International Heritage Center, which opened in 2005 halfway between Truth or Consequences and Socorro, features exhibits and artifacts that commemorate the road’s importance to the Southwest.