The Greater Philadelphia World Trade Center a 3,000,000 sq.ft. mixed use project at Delaware & Callowhill ( World Trade Square in Old City on the riverfront ) is planned  to begin construction in 2007; the first phase , a 400 - unit apartment building and mixed use retail, office and commercial development is sponsored by the DRPA and developed by WRA, a joint Venture of Carl Marks & Co. and entities represented by Silver & Harting.