Qashliq, Isker or Sibir (Siberian Tatar: Iskәr) was a medieval (14th–16th century) Siberian Tatar fortress, in the 16th century the capital of the Khanate of Sibir, located on the right bank of the Irtysh River at its confluence with the Sibirka rivulet, some 17 km from the modern city of Tobolsk.
In 1582 the troops of Cossack ataman Yermak seized and ruined Qashliq.
The ruined city was retaken by the Siberian Tatars in 1584 only to be lost forever in 1586.
Sources of the early 19th century claim that the ruins of the fortress could still be made out with difficulty.
[3] The modern village of Sibiryak (поселок Сибиряк) is located close to the site.