The four Shield Islands, Greenshield, Southshield, Oakenshield, and Greyshield, sit athwart the mouth of the Mander, and for a thousand years and more their lords have kept longships of their own to bar that great river against reavers from the sea. So long as the shield islanders held their waters, the soft green heart of the Reach lay safe behind them. When Euron Greyjoy, newly crowned upon the driftwood throne and styling himself lord of the Iron Islands, turned his ambitions southward, it was the Shields he chose to seize, and with them the key to the richest lands in Westeros.
The ironborn fell upon the islands in strength, the Iron Fleet under Euron's brother Victarion driving before it the smaller squadrons of the shield lords. The islanders were overwhelmed, their longships taken or burned, their keeps stormed, their lords slain or scattered; Euron parceled out the conquered halls and their women among his captains as spoils. With the guardian isles thrown down and their fleets destroyed, the mouth of the Mander lay open, and the reavers poured up the undefended river in their hundreds.
What followed was less a battle than a harrowing. The ironborn burned and looted their way deep into the Reach, sacking towns and villages that had not seen an enemy in living memory and putting the countryside to fire and the sword while the strength of Highgarden was away at the wars in the south. The maesters count the taking of the Shield Islands among the boldest and most ruinous of Euron Greyjoy's strokes, for it laid bare the soft underbelly of the realm and drew the wrath of the Reach and the Redwyne fleet back upon the ironborn in the season that followed.