He took back with him a great deal of invaluable information on the subject of tides, but the cost of obtaining such knowledge had been by no means small. It is possible that a critical reader may feel disposed to remark that the Channel tides in Cæsar’s time were not identical in direction and force with those of to-day. It is impossible to settle the point with accuracy. Certain it is that for some centuries the coast between Sandgate and Dover has altered a good deal, but, speaking generally, this has not been of much consequence, though a good deal of alteration has taken place between Hythe and Dungeness, which may or may not have affected the tidal stream. Similarly, it is a matter for dispute whether the Channel stream in the neighbourhood of the Dover Straits began to ebb and flow at precisely the same time as to-day. It is more than possible that the changes in the configuration of the coast and of the Goodwin Sands may, during the centuries, have modified the Channel tides hereabouts. Some say that in Cæsar’s time Thanet was an island, that Dungeness did not exist, that Romney Marsh was covered at high water by an estuary 50,000 acres in extent, and that the estuary of the Thames was far wider than to-day. But even when all these points have been taken into consideration, two facts remain true: that the tide ebbed and flowed backwards and forwards along the English Channel, and that because of the narrow neck through which this huge volume of water has to rush by the Straits of Dover there must have been not much difference in strength from that which is experienced to-day. The geographical information which Cæsar brought back concerning Gaul and Britain after his campaigns cannot be lightly regarded. It was the knowledge which an explorer bestows on a wondering community. Such items as prevailing winds, tides, currents, the influence of moon and the nature of harbours along the coast, the depths of water, and so on, might have been appreciated still more had the Romans been as eager for scientific knowledge as they were for organisation and conquest.