This curious structure is at the back end of a commercial building on Fifth Avenue, where it faces the alley called Watson Street. It’s hard to tell from the old maps, but this may be the back end of the building that used to be the Uptown postal station, Pittsburgh 19. The tower is curious for multiple reasons: first, that there is a tower here at all along the alley rather than at the front of the building where it could be seen; second, because it looks as though it was put together from two slightly mismatched halves; third, because of the extraordinarily narrow Romanesque windows that look as though someone was expecting an attack by enemy archers. The upper floor, which is what makes this look like a tower, may be a later addition.
If you enlarge the picture, you will notice a ghost sign on the building next door: Progressive People Want Perfect Liquors. The position of this sign—where it is all but invisible unless you are looking down on it from a distance with a long lens—suggests that it may be even older than the tower that obscures it.