Finally, it is absolutely indispensable to distinguish carefully between periods. This must be stressed, as fundamental confusion has been caused for lack of this precaution. It so happens that the sources which are most helpful to an understanding of Seljukid institutions come from the Mongol period. Since the dynasty continued under the Mongol protectorate and the new masters did not intend to overthrow the old regime, Seljukid and Mongol-Seljukid institutions have generally been treated together as if they were undifferentiated. An investigation which is careful of the distinction clearly shows that in some matters at least the situation is quite otherwise, and thus that the interpretation to be made from the facts under consideration is wholly different from what has been believed.