Nevertheless, the threat from the Rus' in 860 came as a surprise; it was as sudden and unexpected "as a swarm of wasps", as Photius put it.[1] The empire was struggling to repel the Abbasid advance in Asia Minor. In March 860, the garrison of the key fortress Loulon unexpectedly surrendered to the Arabs. In April or May, both sides exchanged captives, and the hostilities briefly ceased; however, in the beginning of June, Emperor Michael III left Constantinople for Asia Minor to invade the Abbasid Caliphate.[2]