How long is the Great Wall of China when its tributary branches are included?

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military engineering Israel Defense Forces armoured combat engineering front loader, 2006.

The total length of all sections of the Great Wall of China ever built, including all tributary branches and overlapping sections, is approximately 21,196 kilometers (13,171 miles).1

While earlier estimates—which excluded these secondary sections and branches—often cited a length of about 4,160 miles (6,700 km), modern surveys and satellite surveillance have provided a more comprehensive measurement of the entire fortification system. It is important to note that this total figure encompasses the various walls constructed over two millennia by different dynasties, rather than a single, continuous structure.21