Large building-like structures on Mars?

The latest series images taken by Mars Rover Curiosity show large building-like structures on top of the mountains.

These ruins are evidence that Mars once was inhabited by intelligent ancient civilizations?

Picture Link: http://mars.jpl.nasa.gov/msl-raw-images/proj/msl/redops/ods/surface/sol/00595/opgs/edr/ncam/NRB_450326956EDR_F0310538NCAM00266M_.JPG

Photo-Group Link: http://mars.jpl.nasa.gov/msl/multimedia/raw/?s=595&camera=NAV_RIGHT_