This image was acquired using the nadir and colour channels of the High Resolution Stereo Camera (HRSC) operated by the German Aerospace Center (Deutsches Zentrum für Luft- und Raumfahrt; DLR) on board ESA's Mars Express spacecraft. The Cydonia region lies slightly to the north of the Martian dichotomy boundary, in the south of Acidalia Planitia. There are numerous mesa-like structures and smaller flat-topped mountains here – the remains of the eroded highland that are spread over large areas of this region. Some planetary researchers believe that parts of these northern lowland plains were once the bed of an ocean or of lakes, which were then covered by layers of lava or sedimentary deposits several hundreds of metres deep.