Why are many streets in the old parts of Chongqing steep and winding?

Many streets in the old parts of Chongqing were historically steep and winding because they were designed to follow the natural topography of the city's hilly landscape.1

The Old City is situated on a rocky promontory of red sandstone and shale, which projects between the Yangtze and Jialing rivers. Because the city was built on this uneven terrain, its early cross streets were narrow and often followed the contours of the hills, with some sections consisting of flights of hundreds of steps to navigate the elevation changes.21