What was standard, though, was the means Americans had of displaying their flags: poles whittled of wood and planted directly into the ground. The most common flag pole in Revolutionary days was simply the trunk of a narrow, felled tree, its shaft pruned and the fabric of a flag tied to its tip. A more advanced version of the tree-as-pole approach found woodworkers processing heartier wood like pine or spruce, shaping the poles with knives and then sanding them to smoothness. The workers would treat the poles with animal fat to act as a preservative, protecting the wood from rotting. Despite that, though, the primitive poles had a generally short lifespan: Even as the viscous layer protected them from the elements, being planted in the ground usually ensured that they would slowly disintegrate from the inside.
In the 1800s, as American industry made its gradual transition from wood-based production to steel, metal became the material of choice for flagpoles. Trolleys and street cars were becoming a more and more common feature of urban transportation; in fabricating the poles that would anchor cable cars' wires, engineers realized that sectional constructions allowed for extra strength. The steel poles used for the trolley wires were often composite structures, with male and female ends connected telescopically. Flag poles, borrowing transportation technology for decorative purposes, employed the same logic. At the World's Columbian Exposition, held in Chicago in 1893, engineers attached a 75-foot steel tube to the existing mast of a ship (itself 95 feet tall). The resulting composite pole -- a crazy concoction consisting of a smooth pole rooted in a knobby mast -- is still in use today, situated on the campus of the University of Michigan.
As American industry expanded in the early 20th century -- and, in particular, during World War II -- innovations like steel shafts for cargo driving and cargo booms on large ships lent themselves to further incremental developments in flag pole design. As a wartime sense of nationalism led to an increased desire for flags and the devices that would display them, an expanding number of flagpole manufacturers used more borrowed technologies to meet the growing demand. Advances in street light and traffic signal manufacture, usually involving new, lighter-but-stronger metals and alloys, led in turn to advances in flagpole design. Flag display continued to benefit from borrowed technology, the ornamental progressing from the practical.
Today, flag poles are so ubiquitous that we barely look at them. As soaring as they are, they're also humble: There are few things more basic -- more primal -- than a stick used to hoist things in the air. But even the most basic structure in the world can always stand to be improved and iterated and modernized. Though the Stars and Stripes long ago adopted an unchanging design, the object used to display it is as variable as technology.
For more on the American flag, see Kasia Cieplak-Mayr von Baldegg's "Know Your Flag! The Evolution of the Stars and Stripes."
Images, top to bottom: steeplejack Jack Tarzan gives the Senate flagpole a fresh coat of paint, July 1939 (via Library of Congress); the World's Columbian Exposition mast-pole, currently at the University of Michigan (via Wikimapia).