Texas is the second most populous and the second most extensive of the 50 United States, and the most extensive state of the 48 contiguous United States. The name, based on the Caddo word "Tejas" meaning "friends" or "allies", was applied by the Spanish to the Caddo themselves and to the region of their settlement in East Texas. Located in the South Central United States, Texas shares an international border with the Mexican states of Chihuahua, Coahuila, Nuevo León, and Tamaulipas to the south, and borders the US states of New Mexico to the west, Oklahoma to the north, Arkansas to the northeast, and Louisiana to the east. Texas has an area of 268,820 square miles (696,200 km2), and a growing population of 25.7 million residents. During the Spanish colonial rule, the area was officially known as the Nuevo Reino de Filipinas: La Provincia de Texas. Antonio Margil de Jesús was known to be the first person to use the name in a letter to the Viceroy of Mexico in 20 July 1716. The name was not popularly used in daily speech but often appeared in legal documents until the end of the 1800s. Houston is the largest city in Texas and the fourth-largest in the United States, while San Antonio is the second largest in the state and seventh largest in the United States. Dallas–Fort Worth and Greater Houston are the fourth and sixth largest United States metropolitan areas, respectively. Other major cities include El Paso and Austin—the state capital. Texas is nicknamed the Lone Star State to signify Texas as an independent republic and as a reminder of the state's struggle for independence from Mexico. The "Lone Star" can be found on the Texas state flag and on the Texas state seal today.