Beginning with the inundation (Summer Solstice) we have—
| (1) | The season or tetramene of the | inundation, July-October. |
| (2) | " | sowing, November-February. |
| (3) | " | harvest, March-June. |
From the earliest times the year was divided into twelve months, as follows, the leading month being dedicated to the God of Wisdom, Thoth (Tehuti):—
| Inundation |  | Thoth | End of | June (Gregorian). |
| Phaophi | " | July. | ||
| Athyr | " | August. | ||
| Choiak | " | September. | ||
| Seed-time | | Tybi | " | October. |
| Menchir | " | November. | ||
| Phamenoth | " | December. | ||
| Pharmouthi | " | January. | ||
| Harvest | | Pachons | " | February. |
| Payni | " | March. | ||
| Epiphi | " | April. | ||
| Mesori | " | May. |
The terms for the seasons and months are found even on the building material of the largest pyramid of Dashûr, and in the oldest records we already find calendar indications. On the steles of the Mastăbas, in which the deceased prays Anubis for a good sepulture, we find a list of the festal days on which sacrifices are to be offered for the dead.
A modern calendar (given both by Brugsch and De Rougé) is, doubtless, a survival from old Egyptian times. It is good for the neighbourhood of Cairo, and the relation of the important days of the inundation to the solstice, in that part of the river, is as follows:—
| Night of the drop | 11 | Payni | ||
| 15 | " | Summer solstice. | ||
| Beginning of the inundation | 18 | " | 3 | days after. |
| Assembly at the nilometer | 25 | " | 10 | " |
| Proclamation of the inundation | 26 | " | 11 | " |
| Marriage of the Nile | 18 | Mesori | 63 | " |
| The Nile ceases to rise | 16 | Thoth | 96 | " |
| Opening of the dams | 17 | " | 97 | " |
| End of the greater inundation | 7 | Phaophi | 117 | " |
In order to show how the astronomy of the ancient Egyptians—to deal specially with them—was to a large extent concerned with the annual flood and all that depended upon that flood; and how the first tropical year used on this planet, so far as we know, was established, it is important to study the actual facts of the rise somewhat closely, not only for Egypt generally, but for several points in the line, some thousand miles in extent, along which in the earliest times cities and shrines were dotted here and there.
Time out of mind the fluctuations in the height of the river have been carefully recorded at different points along the river. In the "Description de l'Égypte" we find a full description of the so-called nilometer at Aswân (First Cataract), which dates from a remote period, perhaps as early as the fifth dynasty.
In Ebers' delightful book on Egypt space is given to the description of the much more modern one located at Rôda.