Two outstanding massive monuments dating back to the Sassanid period are still visible on the territory of Ancient Merw - the Big Kyz Kala and Small Kyz Kala (VI-VII cc).

The Turkic name (in all Turkic languages’ Kyz’ means ‘girl’) probably doesn’t reflect the actual origins or function of the constructions. These rectangular clay castles - ‘Koshks’ have an interesting architecture, decorated from outside with corrugated walls, and various vaults.