Qashliq, Isker or Sibir (Siberian Tatar language: Qasliq or Îsker) 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. The fortress is first mentioned in Russian sources of the 14th century.

Qashliq, Isker or Sibir (Siberian Tatar language: Qasliq or Îsker) 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. The fortress is first mentioned in Russian sources of the 14th century.