The M41, known informally and more commonly as the Pamir Highway (Russian: Памирский тракт, romanized: Pamirsky Trakt), is a road traversing the Pamir Mountains through Afghanistan, Uzbekistan, Tajikistan and Kyrgyzstan with a length of over 1,200 km. It is the only continuous route through the difficult terrain of the mountains and is the main supply route to Tajikistan's Gorno-Badakhshan Autonomous Region. The route has been in use for millennia, as there are a limited number of viable routes through the high Pamir Mountains. The road formed one link of the ancient Silk Road trade route. M41 is the Soviet road number, but it only remains as an official designation in post-Soviet Uzbekistan, as confirmed by official decree. Kyrgyzstan and Tajikistan have passed decrees abolishing Soviet numbering of highways and assigning their own national numbering.