34°18′30″N 108°51′30″E / 34.30833°N 108.85833°E / 34.30833; 108.85833

Chang'an, located in China's Shaanxi Province, was the capital city of several Chinese dynasties, including the Western Han and the Tang, from 202 BC to AD 907. At various times, it was the largest city in the world. Its name was subsequently changed, and during the Ming dynasty period its modern name of Xi'an was adopted.

The site of Chang'an south of the Wei River in central Xi'an has been inhabited since Neolithic times, when the Yangshao culture had a major center at Banpo to its south during the 5th millennium BC. Fenghao, the twin capitals of the Western Zhou, straddled the Feng River to its southwest from the 11th to 8th centuries BC and the state of Qin and its imperial dynasty had their capital in nearby Xianyang, north of the Wei, in the 4th & 3rd centuries BC. The First Emperor's mausoleum and its Terracotta Army lay to its east.

Liu Bang moved his court to the Changle Palace in 200 BC, soon after the establishment of the Western Han. It held a central position in the large but easily defended Guanzhong Region, near but outside the ruins of the Qin Xianyang and Epang Palaces. Han Chang'an grew up to the north of it and the adjacent Weiyang Palace. Weiyang continued to serve as the imperial palace of the Xin, late Eastern Han, Western Jin, Han-Zhao, Former Qin, Later Qin, Western Wei, Northern Zhou, and early Sui dynasties and became the largest palace ever built, covering 4.8 km² (1,200 acres)—nearly seven times larger than the Forbidden City—before its destruction under the early Tang. The main areas of Sui and Tang-era Chang'an was south of the earlier settlement and southeast of Weiyang. Around AD 750, Chang'an was called a "million-man city" in Chinese records; most modern estimates put the population within the walls of the Tang city around 800,000–1,000,000. The 742 census recorded in the New Book of Tang listed the population of Jingzhao, the province including the capital and its metropolitan area, as 1,960,188 people in 362,921 households and modern scholars—including Charles Benn and Patricia Ebrey—have concurred that Chang'an and its immediate hinterland could have supported around 2,000,000 people.

Amid the Fall of Tang, the warlord Zhu Wen forcibly relocated most of the city's remaining population to Luoyang in 904. Chang'an was of minor importance in the following centuries but again became a regional center under the Northern Song. Its name was changed repeatedly under the Mongol Yuan dynasty before the Ming settled on Xi'an and erected its city walls around the former Sui and Tang palace district, an area about an eighth the size of the medieval city at its height.

The site of Chang'an south of the Wei River in central Xi'an has been inhabited since Neolithic times, when the Yangshao culture had a major center at Banpo to its south from around 5000 to around 4300 BC and other sites in the area for several more centuries. Fenghao, the twin capitals of the Western Zhou, straddled the Feng River to its southwest from c. 1064 to 771 BC and the state of Qin and its imperial dynasty had their capital in nearby Xianyang, north of the Wei, from 350 to 207 BC. The First Emperor's mausoleum and its Terracotta Army lay beside Mount Li to its east. Chang'an itself existed as a small village under the Qin.

Upon the Fall of Qin and the resolution of the Chu–Han Contention with the establishment of the Han dynasty in 202 BC, the emperor Liu Bang (posthumously honored as its Emperor Gaozu) initially ruled from Luoyang, the site of the Eastern Zhou capital Chengzhou and supposed center of the world. This was in accordance with the majority of his advisors, themselves mostly from eastern China. Upon reflection, however, he heeded the advice of a soldier Lou Jing and his general Zhang Liang that the Guanzhong Region—the Zhou and Qin heartland along the Wei River—could provide for a larger core population and offered much greater natural protection against potential unrest. Additionally, Chang'an was far more centrally located in the lands directly administered by the Han emperor and much further from their border with the realm's notionally vassal kings.

Liu Bang commissioned his chancellor Xiao He to rehabilitate the Qin's Xingle Palace (興樂宮, "Palace of Flourishing Happiness") for use as his primary court in the 9th month of Year 5 of his reign as king of Han (202 BC). This was completed as the 7×7 li Changle Palace in the 2nd month of Year 7 (200 BC), by which time Xiao He had already begun renovating the Zhangtai Palace (章台宮, "Palace of the Splendid Terrace") as the 5×7 li Weiyang Palace. According to Sima Qian's Records, Liu Bang returned to Chang'an in that year, initially reproaching his minister for the needless extravagance of constructing such enormous palaces in such close proximity to one another. Xiao He successfully argued, however, that the magnificence was necessary to overawe Liu's rivals and affirm the legitimacy of the dynasty. Around the same time, thousands of clans in then military aristocracy were forcibly relocated to the region. The minister Liu Jing described this policy as "weakening the root while strengthening the branch", but it served to keep potential rivals where they could be more easily observed and redirected their energy towards defending the new capital against the nearby Xiongnu. The Weiyang Palace was initially completed in 198 BC, but Liu Bang continued to rule from the Changle Palace for the remainder of his life. Subsequent emperors ruled from Weiyang while using Changle to house their mothers, wives, and concubines. An arsenal was placed directly between the two palaces to protect them and the nascent city.