Great Northern War
In the early 18th century Russia and Sweden were both infested with the plague and at war with each other. The Swedish city of Reval (now Tallinn) in the region of Estonia was attacked by a Russian force of over 5,000 men. Reval was a walled city on the shores of the Gulf of Finland. It was overcrowded with refugees who had fled behind its walls to escape the approaching Russian Army, which had merrily destroyed all the villages and farms it had encountered during its approach.
By the time the Russian Army arrived before Reval’s gates, the walls of the city were sheltering nearly 20,000 people, with limited sanitation facilities available, overcrowded and unprotected. To make their presence and intentions clear, the Russians catapulted the bodies of many of the Swedes they had encountered during their march to Reval, and many of these were victims of the plague. The infected dead thus added to the strained conditions, (they probably didn’t help morale much either) and the lice and fleas carried in the clothing and hair of the dead soon found new living bodies on which to feed, spreading the disease within the overcrowded city.
Reval surrendered to the Russians before they launched a full attack, on the 30th of September. The Russians then chose to remain outside of the city which they had deliberately bombarded with disease. Within 10 weeks, the living population of Reval was reduced to less than 2,000 with more than 15,000 having succumbed to the plague.
Those who had been allowed by the Russians to leave fled to other cities in Europe, in many cases taking the plague with them to their destination. A large number of these fled to nearby Finland, which was soon being ravaged by the disease, with over 60% of the population of Helsinki dying of the disease before the end of the year.