The Atlanta Beltline and Trees Atlanta are celebrating a major environmental milestone as their partnership transforms the city’s historic rail corridors into a world-class botanical destination. The project, known as the Atlanta Beltline Arboretum, was recently designated the world’s longest linear arboretum. As of this spring, the arboretum spans 12.44 miles of completed trail, and the two organizations are working toward an ambitious goal to reach 16.7 miles by this summer.