Rodeph Shalom, the crenellated limestone redoubt between Green and Mount Vernon Streets, has been one of the unexpected beneficiaries of Center City’s recent surge in population. The stately synagogue has added so many new congregants in the last decade that its Sunday-school enrollment has doubled to 300 and its membership roster stands at 1,150 families. Despite having a location just outside the traditional boundaries of downtown, it now likes to boast that it is Center City’s largest synagogue.