Merry-Met Under the Mistletoe
Druids and Romans both held mistletoe in high regard. These groups believed that the plant had healing powers and could ward off evil. Mistletoe was seen as a connection between earth and the heavens because it grew without roots. It was also a symbol of peace – stories tell of soldiers holding a temporary truce if they met their enemies under mistletoe. Ancient Britons thought that hanging mistletoe at their door would keep evil from it. Anyone who was able to cross the threshold safely received a welcome kiss, thus starting the Christmas tradition of kissing under the mistletoe.
-from https://www.ancient-origins.net/history-ancient-traditions/mistletoe-holly-and-yuletide-cheer-weaving-natural-elements-ancient-021772
