The chiseled and scorched area to the right of the man is where a five line ancient Hebrew inscription was found in 1880. The inscription is now in the Archaeological Museum in Istanbul. Click Here to view the inscription.
The inscription describes how two groups of men began working at each end of the tunnel and how, after a bit of difficulty, they met in the middle. At that time the water began to flow from the Gihon Spring to the Pool of Siloam and has ever since!
For another view and a more complete description of the tunnel Click Here.
For a translation of this inscription see Arnold, Bill T., and Beyer, Bryan E. eds. Readings from the Ancient Near East: Primary Sources for Old Testament Study. Grand Rapids, MI: Baker Books, 2001, p. 171-72. To view for possible purchase Click Here.