A phenomenon of square and circular geoglyphs dating to the 1st-2nd millennium AD has been revealed by means of deforestation and aerial photography in the past decade. News reports on discoveries of this phenomenon can be found here, here, here, and here. An article on this phenomenon is here.

A screenshot of the area where the geoglyphs are found:

A closer screenshot:

Most walls of squares measure between 10 and 240 meters in length, and most diameters of circles are about the same size.

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