In a world of rapid growth in maritime trade, understanding the tides was vital. Yet it was a complex process, dependent on science, geography, mathematics, religion and ego, writes Hugh Aldersey-Williams.

When Julius Caesar’s invasion of Britain was under way in September 54 bc, Marcus Tullius Cicero wrote from Rome in reply to a letter from his brother Quintus, who was accompanying Caesar. The letter had spoken of the apprehension the Romans felt about tidal shores: ‘How glad I was to get your letter from Britain! I was afraid of the ocean, afraid of the coast of the island. The other parts of the enterprise I do not underrate; but yet they inspire more hope than fear.’

Accustomed to the small tides of the Mediterranean, the Romans had reason to be fearful. Both of Caesar’s landings, in 55 and then 54 bc, were hampered by the strong, unfamiliar tides of the English Channel. ‘The Deified Caesar crossed over to the island twice’, the geographer Strabo relates, ‘although he came back in haste, without accomplishing anything great or proceeding far into the island, not only on account of the quarrels that took place in the land of the Celti, among the barbarians and his own soldiers as well, but also on account of the fact that many of his ships had been lost at the time of the full moon, since the ebb-tides and the flood-tides got their increase at that time.’

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Time and Tides

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