This chapter advances the hypothesis that the heightened eschatological sensitivity evident among historians writing in the 5th century, and its weaker echoes in the time of Charlemagne, were caused by irregularities in the lunisolar calendar and its particular realization, the Easter calendar. The lunisolar calendar that Christians used to calculate the date of Easter had a number of key periods when the cycles of the Sun and the Moon came in sync in relationship to the beginning of the count, resulting in the times repeating themselves or ending with nearly precise astronomical repetition. In this chapter, several key lunar cycles that stemmed from the harmonics of the Moon's precession on its orbit around the Earth are outlined on the basis of modern astronomical data and with the help of simple mathematical calculations. It is suggested that the conjunctions of the solar and lunar calendars fell on the 1st as well as the late 4th and 5th centuries CE, with a long hiatus in the 2nd and 3rd centuries. It is argued, at the same time, that there were significant irregularities in the lunisolar calendar that were visible in the 5th century and ca. year 800 CE. These irregularities, when the calendar either lost or added a day due to the imperfections of the Julian calendar and to the lack of knowledge about the true length of the solar and lunar periods, may have contributed in the 5th century and ca. year 800 CE to the heightened expectations of the time (or the lunisolar cycle) reaching its end in disarray. It is suggested that the first episode of facing off with the irregularities of the lunar calendar of Easter holidays came at about 410 CE when the problem caused historians to wonder whether the Heavens all went against the normal course of time. Thus, sensitivity to the eschatological vision of time in the 5th century and ca. 800 CE may be hypothetically explained by the fact that the solar calendar stopped syncing with the lunar calendar and discrepancies arose. © 2025 selection and editorial matter, Israel Sanmartín and Francisco Peña Fernández; individual chapters, the contributors.