The Louisiana Purchase of 1803 doubled the size of the United States and added over 800,000 square miles of territory west of the Mississippi River for $15 million. This culturally and ethnically diverse region had a French and Spanish colonial heritage and followed the Napoleonic Code rather than English common law. Louisiana became the 18th state in 1812 after meeting population requirements through immigration and with a constitution written in New Orleans. Two hundred years later, Louisiana retains a unique culture blending French, Spanish, Catholic, and American influences.