By mid-1572 the Eighty Years' War had reached one of its most precarious moments. The Sea Beggars, Dutch rebels supported by Stadtholder William of Orange and English volunteers sent by Elizabeth I, had taken Brielle in April and most of Zeeland had risen with them. Only four places in the province still held for Spain: Arnemuiden and Middelburg on Walcheren, Goes on Zuid-Beveland, and the fortress of Rammekens. On 26 August, Jerome Tseraarts, governor of Flushing, returned to besiege Goes with 7,000 troops, including 1,500 English under Thomas Morgan and Humphrey Gilbert. The Spanish garrison of Goes under Isidro Pacheco was vastly outnumbered. The Duke of Alba, governor of the Spanish Netherlands, ordered relief by sea from Antwerp. But the Sea Beggar fleet under Ewout Pietersz Worst controlled every navigable channel. Reinforcement by water was impossible.

The solution came from a Fleming named Plomaert, a captain loyal to Spain, who knew the local water. He had grown up among the men who fished and farmed the tidal flats between Brabant and Zuid-Beveland - the great mudbank country where the Scheldt divided into the Oosterschelde flowing north and the Westerschelde flowing west. Plomaert took two local guides and walked the route at low tide himself, mapping the channels. The plan he brought back to Sancho Davila and Cristobal de Mondragon was audacious: at the lowest spring tide of the month, with two hours of slack water, an army could ford the Oosterschelde on foot. The main river channel would still be a meter and a half deep, sometimes deeper. Smaller channels - kreken in Dutch - would intersect the route, deeper still. The men would be in water for ten hours. Mondragon, a veteran in his late fifties, approved the plan.

Mondragon assembled 3,000 Spanish, Walloon, and German pikemen at Woensdrecht near Bergen op Zoom. They set out at low tide on the night of 20 October 1572. The discipline required was extraordinary. The soldiers moved in column with their pikes shouldered above their heads, the guides leading the way through the kreken. Where the channels were deepest, men linked arms to keep from being swept off the route by residual current. The water was cold - October in the North Sea - and the wind was unkind. According to the chronicles, soldiers who lost their footing in the deeper channels mostly recovered, but some drowned. The crossing took the full hours of low water and into the rising tide; by the end the leading ranks were wading in deeper water than they had started in. When the column emerged on Zuid-Beveland near Goes at dawn, no one expected them. No army was supposed to come from that direction. There was no direction from which an army was supposed to come.

The Anglo-Dutch besiegers learned almost immediately that a relief force had arrived in their rear. Tseraarts, facing the prospect of being caught between the Goes garrison sallying out and 3,000 fresh tercios coming from the mudflats, ordered a withdrawal. The English contingent under Morgan and Gilbert pulled back with him. Goes was relieved without a major pitched battle - the very fact of the arrival was the victory. The Spanish then used Goes as a base to push reinforcements into Middelburg, which held out under siege until February 1574 before finally surrendering. At the end of 1572, four places in Zeeland still flew the Spanish flag: Goes, Arnemuiden, Middelburg, and Rammekens. The walk across the sea had bought Spain another year and a half in the province.

Military historians treat the Relief of Goes as one of the most extraordinary feats of arms in early modern European warfare - a march by inundation, the opposite of the Dutch defensive flooding the rebels themselves used so often. Cristobal de Mondragon, who lived another twenty-four years and died at around eighty-two in 1596, was honored as a Spanish military hero; an engraving from 1599 still depicts him in armor. The crossing route is now mostly drowned again under the Oosterschelde, the tidal flats reshaped by storms and by the twentieth-century Delta Works. The town of Goes still sits where the tercios delivered it. The bar across the harbor where the rebel fleet anchored has silted in. The walk itself, accomplished in a single night by three thousand men carrying pikes through the dark over the bottom of the sea, is remembered as the kind of thing the tercios did because no one else had thought to try.