Dizkuh (Persian: دزکوه) or Shahdiz (شاهدز), was a fortress near Isfahan, Iran, notably held by the Nizari Ismailis.

Dizkuh was a fortress in central Persia, located in the strategic route leading to Isfahan, capital of the Seljuq Empire.

[1] The historian Ibn al-Athir attributes the construction of the fortress (which he called the "Fortress (qal'a) of Isfahan") to the Seljuq sultan Malikshah, but it is more likely that it dates back earlier, even as early as the pre-Islamic Sasanian period, and the Seljuq sultan simply rebuilt the castle which was near his capital.

He posed as a schoolmaster and gradually converted the garrison force of the fortress, most of whom were of Daylami origin with Shiite tendencies.

Shahdiz was strategically important as it guarded the main route to Isfahan, the Seljuq capital city.