It was a modern undersea metropolis built 30,000 feet (9,144 meters) below the surface. It featured a variety of buildings, including a large auditorium as well as a hotel with windows that revealed fish outside.
In the year 2266, celebrated Earth mathematician and pacifist Alfred Bleikoff, cryogenically frozen in the 1990s, was revived aboard the USS Enterprise. Once back on Earth, he delivered rousing speeches in Rome, New Chicago and Mariana City, accompanied by James T. Kirk, Spock, Leonard McCoy and Montgomery Scott. It was in Mariana City where Bleikoff first proposed to have the planetary Earth defense screen removed in the name of peace. His presentation overwhelmingly swayed the audience, prompting Spock to consider whether Bleikoff might be using some form of mass hypnosis transmitted through radio waves. Kirk suggested that an alien race intent on invading Earth could have surgically altered Bleikoff while he was frozen. (TOS comic: "Prophet of Peace")
Points of InterestEdit
- Protective Dome
- The city was presumably built on or near the Mariana Trench on the surface of the Pacific Ocean.
- The pressure 30,000 feet below the surface would be a crushing 906.5 atmospheres.  The inhospitable surface of Venus had an average pressure of 93 atmospheres. 
- ↑ http://docs.bluerobotics.com/calc/pressure-depth/
- ↑ https://en.wikipedia.org/wiki/Atmosphere_of_Venus
- Prophet of Peace article at Curt Danhauser’s Guide to Gold Key Star Trek Comics