To understand why Somairle came to Renfrew, you have to picture twelfth-century Scotland as a place of overlapping spheres rather than borders. The Scottish Crown was pushing west, granting fiefs to magnates like Hugh de Morville and Robert de Brus, men brought in to settle and defend the realm against raids out of the Isles. Walter, ancestor of the Stewarts, was given expansive grants along the upper Clyde. The new Scottish castles rising on that river were not decorative. They were a wall of stone aimed at Somairle's sea-roads. From Argyll out to the Hebrides, Somairle ruled a maritime imperium of mixed Scandinavian and Gaelic ancestry, the same blended culture the Lewis chessmen now sit in the British Museum representing. He had already shown what he could do in 1156, when he clashed at sea with the Manx king Guðrøðr and won the southern isles. Now he sailed up the Clyde with everything he had.

Timing matters in war, and Somairle's timing has long puzzled historians. King Malcolm IV of Scotland was sick. The Chronicle of Melrose records that he was stricken with a great sickness in 1163, and may never have fully recovered; the Annals of Ulster, on his death, called him Cennmor, which means Big Head, leading some modern scholars to wonder whether he suffered from Paget's disease. A weakened king meant a weakened realm. Somairle may have read the moment as opportunity. The Norse-backed campaigns his descendants would later mount up the Firth of Clyde in 1230 and 1263 followed something like the same template, and there is even an older shadow behind all of them, the Viking sack of Alt Clut, the great rock of Dumbarton, in 870, when Dublin-based Norsemen broke a rival power that had grown too strong along this same river. Each of these invasions was, in essence, the sea asking whether the inland kings could hold their coast.

The exact ground where Somairle fell is lost. Local tradition, recorded in the late eighteenth century, said his fleet landed at Renfrew and his men marched south to a raised piece of ground called Knock, between Renfrew and Glasgow, where they were broken by the levies of the Scottish magnates. In 1772 the naturalist Thomas Pennant walked the site and described a mound or tumulus with a ditch around its base and a single standing stone on top. People nearby called it Queen Blearie's Stone, attaching it not to the 1164 battle but to a much later tragedy, the death of Marjorie Bruce in a riding accident and the caesarean birth of her infant son, the future Robert II. The antiquary David Dalrymple thought Queen Blearie was a corruption of a Gaelic name meaning Memorial of Battle, and that the stone really did mark Somairle's defeat. Either way, the stone is gone. Part of it was reused as a barn-door lintel, and by the mid-nineteenth century the rest had vanished. A housing estate covers the ground today.

Somairle's death did not end his line. Within a year, his sons divided his imperium among themselves; the Kingdom of the Isles was partitioned, with Guðrøðr regaining his half and Clann Somairle keeping the rest. Over generations, the Stewarts would patiently profit from the infighting among his descendants, until the western fiefs first granted to Walter's family carried his children all the way to the throne of Scotland. But on a day in 1164, the question at the mouth of the Clyde was simpler. A sea-lord with a fleet had asked whether the new kings of the inland could hold this water. The river answered. Whatever else you can say about him, Somairle came in person to ask the question, and paid the price himself.