AN astronomical event recorded on a clay tablet found in 1948 among the ruins of the ancient city of Ugarit, in what is now Syria, was identified 20 years ago as a description of a total solar eclipse that occurred on 3 May 1375 BC1,2. The dating of ancient solar eclipses provides reference points to fix the long-term evolution of angular momentum in the Earth-Moon system3. We have reanalysed the Ugarit eclipse record4. A new historical dating of the tablet, and mention in the text of the visibility of the planet Mars during the eclipse as well as the month in which it occurred enables us to show that the recorded eclipse in fact occurred on 5 March 1223 BC. This new date implies that the secular deceleration of the Earth's rotation has changed very little during the past 3,000 years.