While Alexios I was preparing defences against the attack of Bohemond, a great comet appeared in the sky for 40 days. He asked Basileios, the eparch of the city who had a reputation as an astrologer, what the comet meant. Basileios saw St Ioannes the Evangelist in a dream, and he told him that it signified the Norman invasion of Bohemond, while its extinction meant that the invasion would fail. The comet was also seen by Fulcher of Chartres in Jerusalem, together with other phenomena in the sky during February and March