Archaeologists focussed on the Yellow River valley in Henan as the most likely site of the states described in the traditional histories. After 1950, remnants of an earlier walled city of the Erligang culture were discovered near Zhengzhou, and in 1959 the site of the Erlitou culture was found in Yanshi, south of the Yellow River near Luoyang. Radiocarbon dating suggests that the Erlitou culture flourished c. 2100 BC to 1800 BC. They built large palaces, suggesting the existence of an organized state. More recently the picture has been complicated by the discovery of advanced civilizations in Sichuan and the Yangtze valley, such as Sanxingdui, and Wucheng, of which the traditional histories make no mention.