Note 386 — Chapter VII · (Year of Rome 699.) (Book IV of the “Commentaries.”) INCURSIONS OF THE USIPETES AND THE TENCTERI—FIRST PASSAGE OF THE RHINE—FIRST DESCENT IN BRITAIN—CHASTISEMENT OF THE MORINI AND THE MENAPII.

It is almost impossible to fix with certainty the day when Cæsar quitted Britain; we know only that it was a short time before the equinox (propinqua die æquinoxii), which, according to the calculations of M. Le Verrier, fell on the 26th of September, and that the fleet started a little after midnight. If we admit a passage of nine hours, with a favorable wind (ipse idoneam tempestatem nactus), as on the return of the second expedition, Cæsar would have arrived at Boulogne towards nine o’clock in the morning. As the fleet could not enter the port until the tide was in, it is sufficient, to know approximatively the date of Cæsar’s return, to seek what day in the month of September, 699, there was high tide at that hour at Bolougne. Now, in this port, the tide is always at its height towards nine o’clock in the morning two or three days before full moon and before new moon; therefore, since the full moon of the month of September, 699, took place on the 14th, it must have been about the 11th or 12th of September that Cæsar returned to Gaul. As to the two ships which were driven farther down, Mr. Lewin (Invasion of Britain by J. Cæsar) explains this accident in a very judicious manner. He states that we read in the tide-tables of the English Admiralty the following recommendation: “In approaching Boulogne when the tide is flowing in, great attention must be paid, because the current, which, on the English side, drags a ship towards the east, on the Boulogne side drags them, on the contrary, towards the Somme.” Nothing, then, is more natural than that the two Roman transport ships should be driven ashore to the south of Boulogne.