https://amp-theguardian-com.cdn.ampproject.org/v/s/amp.theguardian.com/science/2024/nov/17/mystery-surrounds-800-year-old-leicester-burial-pit-containing-123-bodies?amp_gsa=1&_js_v=a9&usqp=mq331AQGsAEggAID#amp_tf=From%20%251%24s&aoh=17318459584131&csi=0&referrer=https%3A%2F%2Fwww.google.com&share=https%3A%2F%2Fwww.theguardian.com%2Fscience%2F2024%2Fnov%2F17%2Fmystery-surrounds-800-year-old-leicester-burial-pit-containing-123-bodies
Pestilence would be my guess...
Another article on the same topic
https://www.popularmechanics.com/science/archaeology/a63023701/123-ancient-bodies-garden/