These color photo's, taken by the French during World War I, are simply incredible. They were taken by the Autochrome Lumière process, invented by early French filmakers the Lumière brothers in 1903 and the only commercialy color process available until 1935 when Kodachrone was developed. Incidently, the use of Kodachrome was popularized in the late 1930s by Eliot Porter who was instrumental in the development of the dye transfer process which enabled the creation of brilliant, full color enlarged prints from negatives. I mention this only because Elliot Porter has always been a favorite of mine as well as because I went to law school with one of his children.
Hat tip to Synthstuff.