This paper focuses some previous discussions around Khmer monuments at Koh Ker in the Preah Vihear province, Cambodia. Architectural style of these monuments was once explained as "Art of the North-Eastern School," contrasted with that of Angkor or the North-Western region, especially caused by its triangular pediments with remarquable spiral scrolls at borth ends. However, this hypothesis was denied when a new chronology of Khmer arts was proposed. Through these discussions, this paper points out some unsolved problems around the architectural characteristics of Khmer monuments at Koh Ker and in the "North-East region."