force that attacked his camp. Nevertheless, Rastislav's army followed the Franks and pillaged many of their estates on the river Danube. In 856 Louis the German turned over the command of the southeastern marches of his kingdom to his son, Carloman with the responsibility to hold the Moravians in check. According to the Annals of Fulda, Carloman led a new expedition against Rastislav in 858, but this campaign was also a failure, for Rastislav remained defiant. Carloman even struck an alliance with Rastislav against his father. Pribina, the Slavic dux of Lower Pannonia, died fighting the Moravians in 861, which suggests that Carloman also had conceded this province to Rastislav. In response to the ongoing rebellion of his son and Rastislav, Louis the German negotiated a counteralliance with Boris I of Bulgaria. The king made it seem that he was leading a new campaign against Rastislav, but at the last moment he moved against Carloman, who thus had no choice but to surrender. Mission of Saints Cyril and Methodius In order to increase his maneuverability, Rastislav attempted to curtail the activities of the Frankish missionaries in his realm. For this purpose, in around 862 he turned first to Rome. Having met with no success, he then asked for "teachers" in Constantinople, in order to educate local Moravians as priests. His embassy also emphasized the need for "teachers" capable of working in Slavic language. Rastislav's request was granted when Constantine and Methodius, two brothers who had learned the Slavic dialect spoken in Thessaloniki (Greece), arrived with a few disciples in Moravia in 863. The two brothers undertook the task assigned to them by using the Slavonic language for teaching and for divine mass, and Constantine even created a script for the Slavs. The Frankish clergy soon came to realize that the activities of the two Byzantine brothers represented a threat to their influence. As the Byzantine missionaries enjoyed Rastislav's protection, Louis the German dispatched Bishop Solomon of Constance to Rome where he described how the diocese of Passau had been "fragmented and brought to ruin" by the defection of the Moravians. Louis the German was also planning to launch a major campaign against Rastislav with the support of Boris I of Bulgaria. Although at the last minute the latter pulled out of the campaign, Louis' new expedition against Rastislav was a success. In August 864 Louis the German invaded Moravia, crossing