Washington in the 60s—the 1860s, that is—wasn't a very nice place. For one, it stunk. A canal-turned-latrine ran the course of the National Mall to the Potomac, livestock roamed freely, and horse manure lined the city streets. The city, to be put lightly, was a work in progress. The Capitol dome as we know it today would not be completed until 1866; the Washington Monument was still a stump (Work on it began in 1848 and was halted in 1854. It wouldn't be taken up again until 1877). According to a 2010 Washington Post feature, in the 1860s "saloons and brothels and gambling parlors easily outnumbered restaurants and theaters."
It was a city of contrasts. The decadent architecture of the Smithsonian, Treasury, and White House, cast amid the backdrop of a sprawling swamp, gave hints at what the National Mall could become. But we weren't there yet.
Below, via the Library of Congress's digital archive (and a big hat tip to the blog Ghosts of DC), are images of the city taken from the still-incomplete Capitol dome in 1863. Where we could, we matched the images to the same scenes today.
This west-southwest view from the Capitol dome shows the Smithsonian Castle (toward the upper-right side of the frame) in contrast to its surroundings. To the right of the Smithsonian, you can make out the very faint stump of the Washington Monument. Independence Avenue runs down the left side of the frame. In the background is the Potomac River. (Library of Congress)
Here's that same shot today. Notice how much farther away the Potomac River appears (more on that below). (Chet Susslin)
One of the biggest differences betweent today's National Mall and the Mall of the 1860s is the size of it. This map of the city from 1850 shows that the current site of the Lincoln Memorial was underwater while he was alive. In the decades to follow, argriculutral sediment from upstream would deposit on the banks, streching the Mall out into the river. The site of the Washington Monument is now about a mile farther from the water than it was when the city was planned. (Via Library of Congress)
In the 1860s, the Capitol dome was not yet complete. But, as shown in the photo above, D.C. still had an operating canal system connecting the Anacostia River to the Potomac. The route of the canal can be seen here, but it essentially drove due east from the Potomac along the Mall, and then to the south toward the Anacostia. And it stunk; people would use the channel as a public dumping ground. Yes, the Capitol grounds were literally a cesspool of human waste. The canal was shut down in the 1870s, and it later became Constitution Avenue.(Library of Congress)
Before we had a sewage-strewn canal that reeked to high heaven. Couldn't do much reflecting in that. Now, we have a proper reflecting pool. (via Flickr/ dannymac15_1999)
A view from the Capitol dome looking north. Notice there's no Union station. That was finished in 1907. (Library of Congress)
Here's what's north of the Capitol today (granted, this view is more northeasterly than due north). Union Station is at the far-left corner. (Chet Susslin)
In 1863, the southeast view down the dirt-paved Pennsylvania Avenue was sparse. The next two pictures show the development of the area over the next 150 years. (Library of Congress)
Here's a similar southeasterly view of Pennsylvania Avenue taken in the 1880s (Pennsylvania Avenue is shifted to the right in this frame). Those white homes in the foreground would be demolished to make way for the Library of Congress, which would come to dominate this scene in 1897. (Library of Congress)
And here's that view in 2007. (Library of Congress)
CORRECTION: An earlier version of this story misidentified the date of the last photo. It was taken in 2007.