Hundreds of peace activists on Monday launched an on-foot march from Berlin, Germany to Aleppo, Syria in hopes of building political pressure to end the fighting and help refugees there.

The Civil March for Aleppo is expected to take a little over three months, and is set to stretch through the Czech Republic, Austria, Slovenia, Croatia, Serbia, the Former Yugoslav Republic of Macedonia, Greece, and Turkey, euronews reported. That’s the so-called “refugee route,” taken backwards, the group wrote on its website. More than a million people took that path in 2015 to escape from battlefields in the Middle East.

The group’s end goal is to eventually reach the besieged city of Aleppo.

“The true purpose of the march is that the civilians in Syria get access to humanitarian aid,” said organizer Anna Alboth, a Polish journalist. “We are marching to build pressure.”

About 400 people set off from Berlin, hoisting white flags and dressed to shield themselves from a dreary winter day. The march began at the former Tempelhof Airport, which was shuttered in 2008 and now serves as a temporary shelter for thousands of refugees from Syria, Iraq, and other countries.