Barnum did not enter the circus business until late in his career (he was 61). In Delavan, Wisconsin in 1871 with William Cameron Coup, he established "P. T. Barnum's Grand Traveling Museum, Menagerie, Caravan & Hippodrome", a traveling circus, menagerie and museum of "freaks", which by 1872 was billing itself as "The Greatest Show on Earth". It went through various names: "P.T. Barnum's Travelling World's Fair, Great Roman Hippodrome and Greatest Show On Earth", and after an 1881 merger with James Bailey and James L. Hutchinson, "P.T. Barnum's Greatest Show On Earth, And The Great London Circus, Sanger's Royal British Menagerie and The Grand International Allied Shows United", soon shortened to "Barnum & London Circus". Despite more fires, train disasters, and other setbacks, Barnum plowed ahead, aided by circus professionals who ran the daily operations. He and Bailey split up again in 1885, but came back together in 1888 with the "Barnum & Bailey Greatest Show On Earth", later "Barnum & Bailey Circus", which toured the world. The show's primary attraction was Jumbo, an African elephant he purchased in 1882 from the London Zoo and who died in a train wreck. Jumbo eventually became the mascot of Tufts University, in honor of a donation from Barnum in 1882.
Barnum was the first circus owner to move his circus by train, and the first to purchase his own train. Given the lack of paved highways in America, this turned out to be a shrewd business move that enlarged Barnum's market. Many circus historians credit Bailey with this innovation. In this new field, Barnum leaned more on the advice of Bailey and other business partners, most of whom were young enough to be his sons.