Warmatrix

The siege of Paris is a showcase of how economical and political interests can direct a battle, or in this case a siege. It was also important in deciding the fate of Paris and the Frankish empire.
In the middle of the 9th century CE, Danish vikings attacked and sacked the city of Paris several times, in 845 CE, 857 CE and 861 CE. Afterwards most of their attention was directed at England, but in 885 CE, after raiding northwest France for some years, they returned with the largest fleet the Franks had ever seen, maybe some 200 ships. In the meanwhile the Franks had strengthened their defenses by building two bridges across the Seine river, which were so low that even the viking longships could not pass under them. Odo, count of Paris, had further reinforced these by a tower each on the outer river bank. The fortifications were strong, but his armed forces were pitifully small.
The Vikings, who arrived in November, demanded tribute. This was denied to them and soon they moved in. The first attacks, possibly with siege engines, later supplemented with battering rams and sapping, were aimed at the northeast tower, which was not completely finished. Despite all the efforts, they were repulsed and during the night the Franks added an extra storey to the building. Another multi-pronged attack at the tower, the bridge, and the city proper was beaten off also and then the Vikings settled down for a long siege. After two months they tried to fill up the river shallows with debris and dead bodies and sent fire ships against the bridge, which was made of wood. This attempt did not break it, but weakened it and later rains caused it to collapse.
Still, the attackers could not break into the city. A part of the army remained to guard it, while the rest set off to plunder the countryside. In the spring Odo managed to break out, call for aid and then break in again. The help came from Henry, the count of Saxony, but his army was weakened by the winter march and could manage only a feeble counterattack, then quickly retreated. However the morale of the besiegers was also low. The viking leader Siegred managed to wrangle 60 pounds of silver from the Parisians, but this was not enough to buy off the rest of the force. Several other leaders, including Rollo, future count of Normandy, stayed put. In the summer they made a last desperate attempt to storm the city, which failed once more. Finally, in October, the main Frankish army under Charles the Fat arrived on the scene and scattered the Vikings. The emperor could have wiped them out, but instead allowed them to sail up the Seine into Burgundy, which was in revolt against him. The Vikings ravaged that area and a year later withdrew with loot and a sum of 700 pounds of silver from Charles. So despite failing to win the siege, they got what they came for.
Looking back, the bridges, though not functioning perfectly, were vital in holding off the vikings. Credit goes to the people in and around Paris who built them and defended them, on their own. This lesson was not lost on them. When Charles died in 888 CE, the French remembered his manipulations, both during the siege and in the years before. They elected Odo as king, made Paris their capital and split up from the eastern areas in Germany. This ended the Carolingian dynasty and the Frankish empire; the Franks became the French.