The Great Wall of Qi (simplified Chinese: 齐长城; traditional Chinese: 齊長城; pinyin: Qí Chángchéng) is the oldest existing Great Wall in China. Construction of the wall started in 685 BC (during the Spring and Autumn Period) by the state of Qi, to defend itself against an invasion by the Kingdom of Chu. The existing sections date back to 500 BC. Construction ended during the Warring States period. The wall stretches from the areas under the administration of the present-day city of Jinan to the present-day city of Qingdao across the territories of the present-day cities of Tai'an, Zibo, Laiwu, Weifang, Linyi, and Rizhao. Its total length has been estimated at about 600 kilometers.