Passing the entrance to 10 Rittenhouse Square on 18th Street in Philadelphia today I was caught up short. Robert A. M. Stern Architects, who designed the 33-story apartment tower, have done something cunning. The entrance to the tower is distinctly low key, a simple break in a low stone wall, flanked by two piers topped by stone balls. Beyond the break, a short path leads to a glass marquee over the front door. It was the wall that interested me. 10 Rittenhouse Square’s immediate neighbor is the Fell-Van Rensselaer mansion, designed in 1898 by the great Boston firm, Peabody & Stearns. The Indiana limestone exterior is rather grand. The new limestone wall, which significantly overlaps the two properties, gives the impression that it was originally a part of the mansion. Thus the entrance to  number 10 becomes integrated with its older neighbor, despite the fact that the apartment tower itself is brick, not limestone, and does not exhibit similar architectural features. A very nice detail.