Reading
The Face on Mars
A 1976 Viking photograph of a mesa in Cydonia looked like a face. Later cameras showed a hill.
ESA & MPS for OSIRIS Team MPS/UPD/LAM/IAA/RSSD/INTA/UPM/DASP/IDA, “OSIRIS Mars true color”, CC BY-SA 3.0 IGO, via Wikimedia Commons
Mars Global Surveyor imaged the mesa in 1998 and 2001, and Mars Reconnaissance Orbiter later at higher resolution. The face was a trick of low light and low resolution. It is a worked example of a reading the ground has since answered, and a reminder that a shape is not a structure. Nothing built has been found on Mars.