An interesting story from The Telegraph. Archaeologists have discovered hundreds of earthworks, similar to the one pictured above, in Acre state in the western Brazilian Amazon. According to the scientists, the earthworks date from around 1 A.D. (the article says the year zero, but there is no year zero). They don't know what the causeways and ditches were for, but theorize that they might be something similar the henge sites (including Stone Henge) in England, which were ritual gathering spots. However, the description of the sites--"with an outer ditch and inner wall enclosure"--makes me think of fortifications. Or, it could be as mundane as serving a purpose similar to digging a shallow trench around a tent to draw off rain water.