What would Philadelphia look like as the capital of the US?

Actually, the state capital left Philadelphia in 1799 when it moved to Lancaster. I've yet to figure out exactly WHY it left Philadelphia, but it doesn't seem related to anything happening at the national level. So it's highly likely that if the federal government located itself in Philadelphia, the state government of Pennsylvania would move.
Like Virginia (Jamestown to Richmond), North Carolina (Wilmington to Raleigh), South Carolina (Charleston to Columbia), and Georgia (Savannah to Atlanta), Philadelphia moved its capital inland to a more location more defensible from powerful foreign navies, and to encourage settlement to the interior of their state.

In regards to Philadelphia remaining the federal capital, I think we could likely expect a massive Haussmann-style renovation of the city in the 1860's-1890's. Philadelphia's ore is small and cramped, it would be absolutely necessary, especially if the federal government expands dramatically in the same time period like it did OTL. Of course, a lot of the expansion was related to the Civil War and what came after, so any TL with a comparable civil war would likely see the same type of expansion. But seriously--something similat to the renovation of Paris is bound to happen, even if on a smaller scale. But I think it's more likely to be equally grand, to make space for the capital of a large nation. Unless the federal government has a late-game move to a Philadelphia suburb.
 
In terms of architecture, Jefferson would still have brought the Greek revival style to some new buildings.

Look at some of the populations. Washington and Philadelphia are today metro areas of 6 million each. Philly itself has 1.5 million, DC only 700,000. The population of Philadelphia did not top 100,000 until after 1840, so there would have been ample "room" for expansion outside the central part of the city. Perhaps Pierre L'Enfant could be the architect who lays out the streets of a new "capital district."
 
The architecture is very interesting and actually helpful to a project I have sort of in the works, but what about administration of the city? I don’t think you can remove Philadelphia from Pennsylvania, so no Capital District. That means that the federal government lies within a state. Would that really have any effects? Or would it just sort of be written off and not worried about too much? The city would obviously work very differently from DC in this regard, but could amount to just working like any other city.
 
The architecture is very interesting and actually helpful to a project I have sort of in the works, but what about administration of the city? I don’t think you can remove Philadelphia from Pennsylvania, so no Capital District. That means that the federal government lies within a state. Would that really have any effects? Or would it just sort of be written off and not worried about too much? The city would obviously work very differently from DC in this regard, but could amount to just working like any other city.
Perhaps the national buildings are, as several people have posited, constructed a fair distance from the commercial/state administrative center, and only that outlying district is ceded to form a federal district?
 
Perhaps the national buildings are, as several people have posited, constructed a fair distance from the commercial/state administrative center, and only that outlying district is ceded to form a federal district?

I don’t see them wanting to really build away from a city though. There’s a reason that hey built a whole new city in DC and not just administrative buildings. They need people, supplies, places to live, and transit at this time makes a suburban administrative center far more difficult.
 
I don’t see them wanting to really build away from a city though. There’s a reason that hey built a whole new city in DC and not just administrative buildings. They need people, supplies, places to live, and transit at this time makes a suburban administrative center far more difficult.
They didn't really build a city though. DC had little urban infrastructure and a small population until well after the civil war.
 
They didn't really build a city though. DC had little urban infrastructure and a small population until well after the civil war.

It was still 14,000 people in 1800. Not a huge population by any means, but more than you would be able to get if you built the capitol center decently outside the city.
 
In terms of architecture, Jefferson would still have brought the Greek revival style to some new buildings.

My point was less that than "if you look at the trajectory of public buildings in Philly you see a pretty similar shift from Georgian to Federalish to Greek Revival, and DC went through a similar early phase if you look at surviving private houses plus destroyed federal building". Also, when DC was still being "built', Pennslyvania offered to build a statehouse and executive mansion so that's a vote for the new administrative area/buildings. Not sure who'd design them though.
 
It was still 14,000 people in 1800. Not a huge population by any means, but more than you would be able to get if you built the capitol center decently outside the city.

I think you're looking at the figure for the District, not Washington City. See https://www.census.gov/population/www/documentation/twps0027/tab03.txt

EDIT: So basically the question is: "At what point does the staffing of the federal government get big enough that the services of Philly don't really accommodate it well and can we pin it at a point before butterflies make it hard to project anything long-distance?" This is probably a bit separate from the narrow question of administrative space etc.
 
Having the U.S. government housed within a state is no big deal. The status would be the same as with U.S. military installations, immune to certain state regulations. There was a time when uniformed servicemen could buy beer on base, even if they were under the state drinking age.
 
I think it was a bigger deal for certain of the Framers in 1790 given what Madison said in Federalist no. 43 but it's not as big an issue now and maybe if a nice enough package is in the offing...

The biggest issue is Southerners not being happy with this frankly.
 
Having the U.S. government housed within a state is no big deal. The status would be the same as with U.S. military installations, immune to certain state regulations. There was a time when uniformed servicemen could buy beer on base, even if they were under the state drinking age.

I think it was a bigger deal for certain of the Framers in 1790 given what Madison said in Federalist no. 43 but it's not as big an issue now and maybe if a nice enough package is in the offing...

The biggest issue is Southerners not being happy with this frankly.

If the capital were to be located in Philly (or any other city in an existing state), I think that that is exactly what would happen, it would be in the state (and maybe the citizens living in the capital city would be considered citizens of the state and vote on those elections and be able to vote for the president etc), but the city itself would be considered a special zone and exempt to certain state issues as well.

And Roger II, I think the biggest issue WOULD be the southerners. Would they have been able to be okay with a "northern" capital from the get-go?

Now, if the capital at DC is abandoned after the War of 1812, Philadelphia is a good candidate and it wouldn't have been that long since the capital left Philly anyway, and by that point the Pennsylvania state capital would already be gone.

If the capital starts out there from the get-go, there will likely be more thought into the city's development as the capital. If it moves there due to the War, I think that it would take a bit before a more uniform plan is put into place. I like the idea of a Haussmann-style renovation of the city taking place at the end of the 19th century. Could definitely see that sort of thing happening.
 
I think the question is how much growth is acutally created by the capital-there won't be the same need for de novo services.
 
I think the question is how much growth is acutally created by the capital-there won't be the same need for de novo services.

I think initially, not a lot. Like has been pointed out several times, I don't think you would see a massive growth in the capital until after the Civil War (or if that is butterflied away, until the end of the 19th century).
 
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