Columbus is the capital of and the largest city in the U.S. state of Ohio. The broader metropolitan area encompasses several counties and is the third largest in Ohio behind those of Cleveland and Cincinnati. Columbus is the sixteenth largest city in the United States of America. It is the county seat of Franklin County, yet the city has expanded and annexed portions of adjoining Delaware County and Fairfield County. Named for explorer Christopher Columbus, the city was founded in 1812 at the confluence of the Scioto and Olentangy rivers, and assumed the functions of state capital in 1816. The city has a diverse economy based on education, government, insurance, banking, fashion, defense, aviation, food, clothes, logistics, steel, energy, medical research, health care, hospitality, retail, and technology. Modern Columbus has emerged as a technologically sophisticated city. It is home to the world's largest private research and development foundation, the Battelle Memorial Institute; CAS, or Chemical Abstracts Service, the world's largest clearinghouse of chemical information; NetJets, the world's largest fractional ownership jet aircraft fleet; and The Ohio State University, the nation's largest campus.