First built in 7th century B.C., Derinkuyu is 
an ancient underground city,  covering an area
 of about 10 square miles and a depth of 18
 stories.   It was large enough to shelter
 up to 35,000 people AND their livestock.
 Christians later used it to hide from persecution.
Massive circular doors could be
 rolled into place by three men.
  These doors were placed in
narrow hallways.  Once the
enemy was near the door, they
could shoot an arrow through
the hole to defend themselves.

Fresh flowing water, ventilation shafts, living
quarters, schools, shops, tombs, and escape
routes.  They even had sophisticated
communication shafts, allowing people
to whisper from one floor to another. 
People lived in these
underground cities for
weeks at a time.
Posted by Picasa