In 1964, architects from Charles Luckman Associates were considering site-planning schemes for the eastern side of the Prudential Center site. Prudential had signaled its intention to go forward with the development of the eastern half of the site, which would mainly feature apartment buildings. Five of them were planned and a series of models were made to experiment with the location of the fifth tower (shown on far right in image at the bottom). Ultimately, only three apartment towers were would be built. A second office tower took the place of two proposed apartments in the southeast portion of the site. Since the 1990s renovations, of course, many more residential units have been built at the Prudential Center and a new tower is currently planned.