Flags of a dozen nations crown the gilded dome of New York's legendary Hippodrome as horse-drawn carriages and the first sputtering automobiles share Sixth Avenue below — this gloriously colorful pre-linen card from 1910 immortalizes America's largest theater at its spectacular peak, its marquee billing "The Plunging Horses" and "A Yankee Circus on Mars," two of the era's most astonishing live spectacles. The New York Hippodrome, opened in 1905 by Thompson & Dundy, seated 5,300 and boasted a 960,000-gallon tank for its famous diving-horse and high-diving acts — an engineering marvel that made it the talk of two continents. Mailed March 30, 1910, from Schenectady, New York, by a sender named Bertha to Mrs. Edna M. in Popes Mills, N.Y., this unused-message card is a vivid time-capsule of Gilded Age entertainment culture.