"Once a testament to mankind's defiance of Kain's empire, this towering cathedral now stood derelict, the humans who worshipped here, centuries dead. Its architects conceived this tower as a holy weapon against the vampire menace, a colossal instrument of brass and stone. The cathedral's pipes, once tuned to blast a deadly hymn, now stood silent, and these vacant spaces whistled their impotence."
The Cathedral was a landmark in the events of Soul Reaver. Constructed by the humans as a holy weapon of destruction against Kain's empire, it was conceived to blast a deadly hymn which would destroy every vampiric creature on the face of Nosgoth. However, Zephon and the Zephonim murdered its guardians before its purpose was fulfilled. They coccooned themselves in the derelict Cathedral, now "a stifled titan [...] in mute surrender – unwilling host to a parasitic swarm."[Soul Reaver/Miscellaneous]
The Silenced Cathedral was apparently built as a weapon against Kain's burgeoning vampire empire. It's complex arrangement of pipes channelled airflow with such force that when a musical note (of the right frequency) was played through them, it was deadly to vampires who came near. At some point in Kain's empire, the Cathedral was attacked, its inhabitants slain and the weapon disabled. Soon afterward, Zephon and his progeny moved in using the Cathedral as their home. Eventually various vampire worshipping humans also moved in.
When Raziel returned, centuries after his execution, he sought out Zephon after gaining the Soul Reaver as a weapon. He had to manipulate the airflow of the Cathedral to reach the upper spires where Zephon dwelt. When Raziel finally reached Zephon, he discovered that Zephon, like much of his clan had (d)evolved in insectoid fashion, with Zephon claiming that he had become infused with the building, effectively making him immobile, though it is likely he fed on the cocooned humans imprisoned elsewhere in the Cathedral.
The Cathedral is an area that was originally planned to be much larger than it is in the release version of Soul Reaver; along with a few obviously blocked doorways (which led to unfinished puzzles), the original Soul Reaver storyline would have had Raziel returning here with the Amplified 'Kain' Reaver, and ascending to the pinnacle(shown in the opening FMV) to open the remaining sounding pipes so that all vampires could be cleansed from Nosgoth. Part of this original ending to Soul Reaver still exists in Raziel's "Hymn of Death" speech; which is still present in the games files.
The Cathedral's arquitecture is clearly based in a Spiral Minaret - a distinctive architectural feature of mosques. A perfect example of a Spiral Minaret can be seen in the Great Mosque of Samarra .
concept art of the Silenced Cathedral and Pinnacle
promotional render of the pinnacle of the Silenced Cathedral