The focus is on the tower of Qābūs ibn Wušmgīr, Ziyarid ruler of Gīlān between the tenth and the eleventh century CE. In spite of the archaeological evidence, the monument is still considered as a mausoleum by most scholars. However, the tower’s geometrical and mathematical features can reveal the outstanding significance of the building as a time-measuring monument. A new interpretative key for the well-known tower of Gonbad-e Kāvus, based on the major time-reckoning cycles of Iranian world, is proposed. On this basis, it is possible to see how the building quite satisfies three needs at least: a need for dynastical propaganda, an administrative need in a fiscal equality perspective, and an Islamic orthodox need, as far as the accuracy of the daily prayer is concerned.