As probably many of those who have heard the Correspondence with the Admiralty read have not made the subject of Cæsar's Invasion their particular study, it may be useful to state the precise question which the recent survey by the Admiralty was intended to settle. It is well known that the first invasion was in the year B.C. 55, and in the harvest month at the south of England, i.e. in August, and it is mentioned incidentally by Cæsar that the full moon occurred on the fourth day after his arrival. The expression is “post diem quartum quam est in Britanniam ventum” (Bell. Gall. iv. 28); and this, according to the Latin idiom, would mean the fourth day, not exclusive but inclusive of the day of arrival, as in the familiar passage of Cicero, “Neque te illo die, neque postero vidi … post diem tertium veni.” (Cicero, Philip, ii. 35.) The full moon here referred to has been ascertained by exact calculation to have occurred on the night of the 30th August, B.C. 55. The day of Cæsar's arrival therefore was on Sunday, 27th August. He tells us that he reached Britain himself at 10 A.M. and waited for the rest of his fleet until 3 P.M. when he advanced eight miles, with the tide in his favour, “et ventum et æstum uno tempore nactus secundum.” (Bell. Gall. iv. 23); so that, assuming him to have anchored off the cliffs between Dover and Sandgate, if he sailed with the flood-tide he would go eastward towards Deal, and if with the ebb tide he would go westward towards Hythe.