"Pridwen was, according to the 12th-century writer Geoffrey of Monmouth, King Arthur's shield; it was adorned with an image of the Virgin Mary."
https://www.wikiwand.com/en/Pridwen
"One such was ‘’Pridwen’’, His Shield. Although it does not appear in Mallory’s ‘’Le Morte’’ Saga, it does in several other ‘’Period Pieces’’ Said to bear a Bottony Cross and the image of The Virgin Mary, Pridwen was said to cause any Enemy blow by Spear or Sword to shatter (with no damage caused to The Shield)."
https://www.stronghold-nation.com/history/myth/pridwen-the-shield-of-king-arthur
"According to Geoffrey, the shield had the image of the Virgin Mary painted on its front. The design of Pridwen would inspire the shield used by the knight Gawain in the poem Sir Gawain and the Green Knight."
https://workingtheflame.com/mythological-shields/