Emperor Willibald's Flood

Emperor Willibald's reign was full of great events, both tragic and heroic, but the flood that struck the coast of the Imperial Overseas Territories in 1202 remains one of the most devastating. 
The coast of the Overseas was always susceptible to floods, and for that reason the local population erected dikes to stop the threat from the waves. When the imperial armies subjugated the land, the Counts of the Overseas quickly learned to appreciate these measures, and the dikes were painstakingly maintained in good order by all means possible and necessary, sparing the land and the people the wrath of nature.
By 1201, however, the priority of flood control was challenged in one crucial place. The well-fortified great city of Osthaven, the jewel of the imperial overseas possessions, one of the main bases of operations for the imperial fleet, and one of the most important cities across the sea, was besieged for five years by that point. The operations strained the strength of both sides, but the imperial garrison was at a great disadvantage - they were forced from many a defensive position by overwhelming enemy strength, and they were running out of materials to erect new earthworks. Without earthworks, any hopes of holding the by then ruined city were in vain. 
The then-commander of the garrison, colonel Oldwig von Fernwald-Obermarkt, was thus forced to employ extreme measures. He order the dikes around the city to be partially disassembled and turned into fortifications, reasoning that even a flood strikes, it will hurt the besiegers no less than the besieged, if not more.
His situation was desperate, and this almost fatalistic decision is thus somewhat excusable. Sadly, von Fernwald-Obermarkt had no way of knowing what was coming, for the next autumn the sea was more tumultous than anyone remembered in a great many years, and the storm winds were exceedingly strong. Knowing men predicted a great flood coming, but the dikes could not be repaired by that point, as the besieged were confined to their small stronghold of earth, rubble, and bodies in the center of the city and some outlying fortifications to the settlement's immediate south and southeast, which were still not taken for reasons of defensibility and lack of purpose in doing so. 
On the 18th of October, the great flood struck. Storm pushed waves to great height and power, and the dikes in the vicinity were easily broken. The raging waters swept over the nearby lowland plains, claiming thousands of besiegers, and utterly drowned many fortification works that were close enough to the sea. The fortified position in the center of Osthaven, which housed the pathetic remains of the garrison, was also badly battered and partly destroyed by the waves, and no less than a full quarter of the battle-ready men left died or vanished without a trace. 
Despite the damage this flood wrought on the enemy, von Fernwald-Obermarkt was in no position to continue resistance and had to agree to an honourable capitulation four days later, leaving the city, by then reduced to rubble, to the foes and leading the remains of his command home.
However great a blow was the loss of Osthaven was to the imperial standing overseas, the flood was not as devastating to the imperial cause as to their foes, inflicting great damage on the latters' manpower and, most importantly, materiel. No great gain was derived from taking Osthaven, for it was reduced to ruins, and the Imperial fleet by then was based in the recently captured city of Willibaldsburg.

Type

Natural