At www.pasthorizons.com/index.php/archives/03/2011/maya-farming-on-the-edge/ anad at www.uc.edu/news/NR.aspx?id=13335 the web site of the University of Cincinatti. Researchers have been trying to fathom why the Maya built their bustling cities nexts to what is swampland – especially the boggy zone of Tikal in modern Guatemala. They have discovered that when the Maya built their cities, from the 4th century BC to the 9th century AD, the environment was somewhat different to nowadays. There was in effect a shallow lake there, providing water resources, and the boggy zone around the lake was use as a resource as well – providing organic material to feed the soil of the fields, including the peat that had accumulated over time, and the general swamp ooze. The fields grew maize – and no doubt other crops too, and over time fertile soils were created by the addition of the organic material. They were more productive than contemporary European rain fed agricultural fields.