  From 1960's to 1970's, the Chinese Army built some fortified artificial
hills. Some of them are located in the Inner Mongolia, Western China. These
large fortresses are surrounded by moats. For some of them it is still possible
to see earthworks, trenches and ditches, the planning of which could have a
symbolic meaning. We can argue this result form their digital outlining,
obtained after an image processing of satellite images, based on edge
detection.
