Why were the shields of Arthur and knights hanging on a tree Turquine and land?

The shields of Arthur and his knights hanging on the tree in Turquine's land symbolize a challenge to any knight brave enough to rescue those captured by Turquine. This act serves as a display of power and dominance by Turquine, showcasing his conquest over Arthur's legendary knights. It also emphasizes the themes of honor and valor in chivalric tales, inviting heroes to prove themselves by reclaiming the honor of their fallen comrades. Ultimately, it sets the stage for adventures and quests central to Arthurian legends.