" Niaresh" of arch structures in tombs architecture of Khorasan.

"Niaresh" is among the most important and fundamental principles of Iranian architecture which covers statics, architecture, and acquaintance with materials. The buildings remnants from the first centuries until the end of Islamic era of Iran indicate that Iranian architects paid special attention to the vault and arch roofing among different special elements. They assumed the beauty of a building was indebted to accurate favouring of arch structures, "Niaresh". The significance of this matter becomes two-fold when we find out that the main special structure of religious and non-religious buildings of Khorasani, Razi, Azari, and Isfahani architectural methods including rooms of roofed nocturnal mosques, porches, chambers, verandas, the collection of entrance, vestibules, and particularly vaults have been built by making use of arch structures and the fact that without such structures such buildings basically dont have an architectural concept. Because of The importance of the subject, the present paper has tried to introduce the most important current arch structures in building of Khorasan grave tombs during Islamic era by making use of reliable and ancient sources of architecture including "the treatise Arch and Azaj" by Ghiyasaldin Jamshid-e-Kashani. The work is the oldest known source dealing with arch structures referred to by this paper; besides, the most important arch structures which were current in the grave vault structures of Khorasan during Islamic era were introduced during fieldwork.