Dibaj (Persian: ديباج, also Romanized as Dibadj; formerly known as Qal‘eh (Persian: قلعه), Chahārdeh, Chārdeh, and Chehārdeh) is a city in the Central District of Damghan County, Semnan Province, Iran. At the 2006 census, its population was 2,504, in 680 families.