Qala-e-Bost

Qala-e-Bost is a fortress in Bost, Afghanistan, built 3000 years ago. It is located at 31° 30’ 02″ N, 64° 21’ 24″ E near the convergence of the Helmand and Arghandab Rivers, a half-hour's drive south of Lashkargah. Qala-e-Bost is famous for its 11th century decorative arch, which appears on the 100 Afghani note (Afghan currency). The arch is part of the remains of a mosque.
History.
In 2006 construction began on a cobblestone road to lead from the south of Lashkargah to the Qala-e-Bost Arch (known to readers of James A. Michener's "Caravans" as Qala Bist.) As of April 2008, it was possible to descend into an ancient shaft about 20 feet across and 200 feet deep, with a series of dark side rooms and a spiral staircase leading to the bottom. In 2020, restoration work started on the fort.