Actually, I would be very careful anywhere near old city. There is something like 20 acres that are technically under the control of the National Park Service, and carrying a weapon is not allowed there. From what I have read, this would make me think twice about carrying near any of the monuments (constitution center, liberty bell, independence Hall), their adjacent parks, and even the streets that run between them.
You might be able to argue that Chestnut Street between 4th and 5th is City Property, not National Park Service land, but you'd be doing your arguing in a Federal Court house if it came to that.
Be very careful when deciding where to carry in that area.
EDIT
Looks like its 55 acres, and that the law on carrying in National Parks may have changed in 2010. So the above may no longer be true, but it was certainly the case a few years back