A normal year with an intercalary month—What does it mean? Such a curious year cannot theoretically exist. But the Drehem calendar could have such a year once in its short history. This article is devoted to the in all probability only one example of such a seemingly very curious phenomenon which did take place in the third regnal year of Šusin, the fourth king of the III Ur dynasty.<br>According to Drehem texts, years began either with the iti-maš-dà-kú month or with the iti-še-gur₁₀-ku₅. That we find two different systems of calendar in one and the same place, Drehem, has seriously disturbed many eminent Assyriologists as, for instance, F. Thureau-Dangin, H. de Genouillac, B. Landsberger. Of course this kind of coexistence cannot be true, because otherwise it must necessarily have brought inevitable confusions into all spheres of everday life and activities of those days. In fact, both of these two systems were not used simultaneously. One which began with the iti-maš-dà-kú month was used only in the years between the 39th regnal year of Šulgi and the third year of Šusin. On the contrary, the other system beginning with the iti-še-gur₁₀-ku₅ month and thus making the iti-maš-dà-kú month the second was not used until the fourth year of Šusin.<br>This change of the month with which years began leads us to the acceptable assumption that an amendment which made the iti-še-gur-ku₅ the first month must have taken place most probably at the end of the third year. If so, the iti-še-gur₁₀-ku₅ month as first month of the fourth year follows immediately after the month of the same name, i. e. another iti-še-gur₁₀-ku₅ which is the last month of the previous year. What happens, then? A very serious confusion in dating of administrative documents isn't to be avoided. I see a clear trace of scribes' endeavor to avoid such a not always inevitable confusion in their placing an intercalary month in the third year of Šusin.<br>This year has been, however, considered as an undoubtedly pure intercalary year by scholars with no single exception because of its having an intercalary month, i. e. iti-diri-ezem-^dme-ki-gál (-e-ús-sa) ‘an additional (month which follows the) month of the festival of me. ki. gál.’ If this is correct, then the year must have had not 12 but 13 months. But at end of some texts of the year man finds the following colophon: iti-maš-dà-kú-ta iti-diri-ezem-^dme-ki-gái (-e-ús-sa)-šè iti-12-kam. This indicates the absence of the month iti-še-gur₁₀-ku₅ in the year. The insertion of an intercalary month as a very substitute of the normal twelfth month iti-še-gur₁₀-ku₅ and instead the omission of the latter are, in my judgemet, a wise device in order to avoid the above-mentioned possible confusion.<br>How can we prove our assumption true? We find some referrences to some of Nippur festivals among Drehem texts. The ezem-gu₄-si-su festival after which the second month of the Nippur calendar, iti-gu₄-si-su, was named, was celebrated in this city in the second month and animal disbursement for it was recorded in Drehem texts of the iti-šeš-da-kú (in the years Šulgi 46, Amarsin 1, 3, 4, 7, Šusin 1, 2) and iti-maš-dà-kú (in Šusin 7). This shows us clearly that the second month of the Nippur calendar, iti-gu₄-si-su, corresponded to the iti-šeš-da-kú in the period before Šusin 3 and to the iti-maš-dà-kú since Šusin's fourth year. It means the amendment of the Drehem calendar took place in his