Rail

"May God continue the unity of our Country as this Railroad unites the two great Oceans of the world."  
- Inscription on the ceremonial Golden Spike 

The symbolic Golden Spike, staked in Promontory, Utah in 1869, marked the completion of the first transcontinental railroad, joining the Union Pacific Railroad from the East and the Central Pacific Railroad from the west. 

One of the earliest and most impressive of America's great railroad engineering feats, the Horseshoe Curve was built as a means of overcoming a straight-line grade over the geological feature known as the Allegheny Escarpment or Allegheny front, which separates the ridge-and-valley section of Pennsylvania (on the east) from the Allegheny Front (on the west). Such a straight-line route would have made commercial railroad operations unfeasible from both and economic and technical standpoint.

The Granite Railway Company of Quincy was the first commercial railway in the United States. Incorporated in 1826 and designed by Gridley Bryant, the railway relied on horses, rather than steam locomotives, to draw the cars along the tracks. Its primary purpose was to transport granite from Quincy to build the Bunker Hill Monument. 

In the 19th century, New York City was a burgeoning industrial and commercial metropolis - the largest city in the United States and second largest in the world. As the city's population increased, people began to call for construction of an underground railway. Many unusual engineering challenges had to be overcome, not the least of which was construction in a dense urban area. After lengthy legal battles over property rights and the debt limit of the city, ground was broken on March 24, 1900.