Scotland on the holy island of Iona in , the year following the raid on the other holy island of Lindisfarne, Northumbria. In , a large Norse fleet invaded via the River Tay and River Earn, both of which were highly navigable, and reached into the heart of the Pictish kingdom of Fortriu. They defeated Eogán mac Óengusa, king of the Picts, his brother Bran, and the king of the Scots of Dál Riata, Áed mac Boanta, along with many members of the Pictish aristocracy in battle. The sophisticated kingdom that had been built fell apart, as did the Pictish leadership, which had been stable for more than 100 years since the time of Óengus mac Fergusa (The accession of Cináed mac Ailpín as king of both Picts and Scots can be attributed to the aftermath of this event). In , the Britons of the Old North around the Firth of Clyde came under Viking attack as well. The fortress atop Alt Clut ("Rock of the Clyde," the Brythonic name for Dumbarton Rock, which had become the metonym for their kingdom) was besieged by the Viking kings Amlaíb and Ímar. After four months, its water supply failed, and the fortress fell. The Vikings are recorded to have transported a vast prey of British, Pictish, and English captives back to Ireland. These prisoners may have included the ruling family of Alt Clut including the king Arthgal ap Dyfnwal, who was slain the following year under uncertain circumstances. The fall of Alt Clut marked a watershed in the history of the realm. Afterwards, the capital of the restructured kingdom was relocated about 12miles (20km) up the River Clyde to the vicinity of Govan and Partick (within present-day Glasgow), and became known as the Kingdom of Strathclyde, which persisted as a major regional political player for another 150 years. The land that now comprises most of the Scottish Lowlands had previously been the northernmost part of the Anglo-Saxon kingdom of Northumbria, which fell apart with its Viking conquest; these lands were never regained by the Anglo-Saxons, or England. The upheaval and pressure of Viking raiding, occupation, conquest and settlement resulted in alliances among the formerly enemy peoples that comprised what would become present-day Scotland. Over the subsequent 300 years, this Viking upheaval and pressure led to the unification of the previously contending Gaelic, Pictish, British, and English kingdoms, first into the Kingdom of