The common tale for how the Black Death Pandemic spread through Europe is based on the rat and the flea. The rats arrived in European ports from Asia and their plague infested fleas spread through the medieval socities of Europe creating a pandemic that killed millions. The rats then established populations in Europe and their fleas stayed with them. Or did they? Research published in the Proceedings of the National Academy of Sciences journal challenges this hypothesis. Plague outbreaks in Asia seem to correlate with climate periods unfavourable for large rodent populations. This would have forced the fleas to seek alternative hosts, such as humans or camels. These hosts then transported the plague along the Silk Road from which it was transmitted to boats in Black Sea ports. Ten years after the outbreak in Asia, the plague would have arrived in Europe. This suggests multiple transmissions of the plague from Asia into Europe, rather than a European reservoir of plague. Multiple transmission events could also mean multiple strains.