The Great Mosque at Harāat ranks among the largest religious buildings still standing in Iranian lands. In the past it has been referred to as an example of Ghūrid architecture heavily restored at various periods. In fact, anyone standing inside the four-ayvān courtyard and looking at the typical arches (plates I-II) or at the marble columns so similar to the stone work at the Gāzargāh, and the mausoleum of Gawharshād, would be inclined to regard it as a typically Tīmūrid mosque. But as soon as one walks into the ayvān this vault takes on unusual proportions: on each side are passages with remarkably strong pillars; and the points of the arches differ from the usual Tīmūrid modulum. The same is true of the complex passages leading from the eastern façade, almost entirely rebuilt in recent years: here also strong square pillars support arches the spans of which come closer to twelfth- or thirteenth-century models rather than those of the late fifteenth century. It would be unwise, of course, to reappraise the period of such an important structure on the basis of a passing impression; a thorough study on the spot, including the drawing of the over-all plan and elevations, and accurate measurements, is necessary.