III. THE DAY ON WHICH CAESAR LANDED IN 55 B.C.
It is absolutely certain, and is universally admitted, that the full moon which Caesar mentions occurred on the night of August 30-1, 55 B.C.:[2947] to speak more precisely, it occurred at 3 h. 33 m. a.m. on the 31st.[2948] Now, with one or two exceptions, which shall be presently considered, the commentators have concluded that Caesar landed on the fourth day before the full moon, that is to say, on the 27th of August. But any one who has read this article with close attention will have seen that their conclusion rests upon a careless interpretation of Caesar’s narrative. Caesar says that the eighteen cavalry transports sailed from Gaul on the fourth day after he landed in Britain; that when they were approaching the island they were prevented from keeping their course by a storm; that some of them were driven westward down the coast and anchored, but were obliged to run back, in the face of night, for the Continent; and that on the same night there was a full moon.[2949] Whereupon the commentators leap to the conclusion that the day on which Caesar landed was the fourth before the full moon. They forget that what Caesar said was, not that the transports approached the British coast on the fourth day after he landed, but that on that day they started from Gaul. The distinction is important. The transports may have weighed anchor in the night. On all his four voyages Caesar set sail at night; and Strabo says that for vessels sailing from Gaul this was the regular practice.[2950] Let us assume that Caesar landed on the 26th of August. Then, if we adopt, as almost all the commentators have done, the inclusive mode of reckoning, the transports may have sailed from Gaul on the night of the 29th.[2951] On the 30th, in the morning, they would have been approaching Britain. Then came on the storm. On the following night—the night of August 30-1—occurred the full moon.
It may be objected that if Caesar had landed in Britain on the 26th of August, and if his transports had set sail on the night of the 29th, but after midnight—say between 2 and 3 a.m.—he would have said that they set sail not on the fourth but on the fifth day after his landing. I will take note of this objection, but I doubt whether it is valid. In the thirty-third chapter of the Second Book of the Commentaries, after describing the sortie made by the Aduatuci, which took place in the third watch of the night, that is to say after midnight, and their repulse, he goes on to say that ‘on the following day the gates were broken open’ (postridie eius diei refractis portis &c.); in other words, he loosely reckoned the third watch of the night as part of the day that preceded the one which he calls postridie eius diei. It is therefore at least possible, I think it probable, that he landed on the fifth day before the moon which he described as full.
But it has been argued that Caesar may have made a mistake in describing the moon as full. He remarks, as we have seen, that the full moon produces very high tides in the Channel; and he states that on the night of this particular full moon many of his ships were waterlogged by an extraordinarily high tide. But the strongest spring tides, in the eastern part of the Channel, between Dungeness and Beachy Head, occur, not at the time of full moon, but a day and a half later, and east of Dungeness two days later.[2952] Airy,[2953] premising that ‘it is impossible to judge precisely of the day of full moon, either from the appearance of the moon’s diameter ... or from the time of moon-rising’, argues that the moon which Caesar described as full was probably, as a matter of fact, that which produced the spring tide. Accordingly he assumes that Caesar landed on the third day before the full moon.
Airy’s argument, however, is unsound. No well-informed man needs to be told that, long before Caesar’s time, astronomers were able to predict the phases of the moon with sufficient accuracy for all ordinary purposes. Livy records that in 168 B.C. a tribune in the army of Aemilius Paullus told his men that a lunar eclipse would occur on the following night.[2954] It is therefore at least not unlikely that Caesar should have known on what night the full moon which followed his landing occurred. The fact that the extraordinarily high tide occurred on the night which he calls the night of the full moon, presents no difficulty. The tide on the night of the full moon, even though, in normal circumstances, it would not have risen as high as a spring tide, properly so called, would in any case have been unusually high; and under the influence of the gale which Caesar mentions, its height would of course have been increased. Extraordinarily high tides, indeed, have occurred in such circumstances even at neaps;[2955] and it would be just as reasonable to argue that Caesar ante-dated the day in question as that he post-dated it. For, as Airy himself assures us, the moon would have appeared full on the night before it really was so, that is to say, on the night of August 29-30; and if, as Airy assumes, full moon had occurred on the night before that to which Caesar assigned it, he would surely have noticed that the moon appeared full on the two successive nights which preceded what, on Airy’s hypothesis, he called the night of the full moon.
The conclusion is that it is not possible to say with absolute certainty on what day Caesar landed. It is morally certain that he adopted the inclusive method of reckoning.[2956] It is, as we have seen, probable that he landed on the fifth, but he may have landed on the fourth day before the moon which he described as full. It is highly probable that he fixed the day of the full moon correctly; but we cannot be perfectly sure. Accordingly it seems to me probable that he landed on the 26th of August: but he may have landed on the 27th, or possibly even on the 25th.
Nevertheless, I assure the reader that this uncertainty matters nothing. If he will bear with me to the end, he will see that we shall be able, notwithstanding, to determine the place of landing.