Philadelphia has long been an architectural throwback by American standards – a huge but almost entirely horizontal city of rowhouses and sprawling urban landscapes, with only a few towering skyscrapers marking its colonial-era downtown. But a new round of development is threatening to take the city vertical, and while residents and historians are understandably wary of becoming just another overcrowded concrete jungle, there may be some virtue in the towers now rising in the city center. “The new skyscrapers are a largely stylish and urbane group – especially compared with designs in other downtowns. Despite some clumsy assemblages of historical parts, most have the virtue of clean, sleek lines. A few even aspire to artful design.”