Tide and time: Re-dating Caesar’s invasion of Britain

Posted by Jayme Blaschke
University News Service
June 23, 2008

Julius Caesar landed an invasion fleet on the shores of Britain in 55 B.C., expanding the boundaries of the so-called “Known World” and inadvertently sparking a dispute between historians and scientists for centuries to come.

Now, a team of astronomers from Texas State University-San Marcos has applied their unique brand of forensic astronomy to the enduring controversy surrounding the precise location of Caesar’s landfall, concluding that the historically accepted date for the event--Aug. 26-27, 55 B.C.--is incorrect. The Texas State team’s proposed new date of Aug. 22-23, 55 B.C., reconciles all the conflicting evidence and offers both sides of the debate some measure of vindication in the process.

Texas State physics professors Donald Olson and Russell Doescher, along with University Honors students Kellie N. Beicker and Amanda F. Gregory, publish their findings in the August 2008 edition of Sky & Telescope magazine, on newsstands now.

O Caesar, Where Art Thou?

“Most history books say Caesar’s landing date was Aug. 26-27 and he sailed to the northeast of Dover to land on an open beach near Walmer and Deal,” Olson said. “That cannot be correct. The afternoon tidal streams could not have carried his fleet to the northeast on that date.”

The origin of the debate, ironically, lies in the strongest historical evidence: Caesar’s first-hand account of the landing and ensuing campaign, which mentions the phase of the moon and chronicles in considerable detail information regarding time of day, landmarks and distances traveled once his fleet reached the famed white cliffs near present-day Dover. Caesar’s narrative describes how, once the winds and tides were favorable, the fleet sailed seven miles along the coast before finding a suitable beach to put ashore. Unfortunately, the actual direction the fleet sailed is one detail Caesar omitted, and in that single oversight lies the bone of contention.

Because of specific coastal and inland land formations referenced by Caesar, historians such as classics scholar Thomas Rice Holmes and archaeologist Charles Francis Christopher Hawkes have long maintained that the fleet sailed northeast along the British coast, coming ashore near the present-day town of Deal. The terrain to the southwest, they argue, simply does not match Caesar’s descriptions. On the other hand, men of science such as Astronomer Royal George Biddell Airy and Admiralty Manual of the Tides coauthor Harold Dreyer Warburg insisted a northeast voyage was impossible since at the historically accepted date and time of Caesar’s landing the tidal currents would be flowing strongly to the southwest--carrying the Roman fleet in the opposite direction from Deal.  

Deal or No Deal?

The Texas State researchers traveled to Britain in August of 2007 to study the problem first-hand. In a fortuitous set of circumstances, the equinox and lunar cycle coincided to closely replicate the tidal conditions Caesar experienced--such an alignment wouldn’t occur again until 2140. Extensive on-site research including the collection of tide gauge data, GPS tracking in a freely-drifting boat and a host of other factors confirmed that the tidal currents indicated a landing site southwest of Dover, while the topographical evidence supported a Roman landing at Deal.

The first break in unraveling the mystery came via an obscure account of the landing by Valerius Maximus, a Roman writing in the 1st century A.D. In Valerius’ work Memorable Deeds and Sayings: Of Courage, he recounts one Roman soldier’s bravery as the tide was falling during the fleet’s landing. The tide, however, would be rising during the fleet’s landing if the date of Aug. 26-27, 55 B.C. were correct.

The second break came from historian Robin G. Collingwood, who in 1937 identified a probable transcription error in a sequence of dates relating to Caesar’s landing, essentially rendering one of the Roman numerals for four (IIII) instead of seven (VII) or even eight (VIII). Applying Collingwood’s revisions to Caesar’s landing changes the date to Aug. 22-23--and reconciles all the previously conflicting evidence.

“If that’s the case, then everything falls into place,” Olson said. “Three things fall into place: the topography matches the ancient descriptions; it matches with respect to the direction of the tidal streams; and it matches with respect to the water level.

“Our new result is, essentially, the old result--we’re taking the Roman fleet up to Deal and the open beach, but what you read in the history books, that it was Aug. 26-27, that cannot be correct,” he said. “The scientists were right about the tidal streams, and so were the historians about the landing site. With our new result, our new date, everything is reconciled.”