What are two dreams that serve as examples of foreshadowing?

As Arthur slept in his ship cabin, he dreamed that a dragon made of gold and azure fought with a foul boar, and that the sea turned red with their blood. Then, the dragon flew to a great height and came down upon the boar, killing it and sending it into the sea. The king awoke and sent for a wise philosopher to interpret his dream. The philosopher said that the dragon represented Arthur, and the boar represented a tyrant or a giant that would be conquered by the king. Soon after this, they landed at Barflete in Flanders.

This is the first in a series of prophetic dreams, a theme which is often repeated in the text. Arthur's dreams usually give an indication of England's state, which reinforces his connection to the land. Here, Arthur dreams of a dragon which defeats a boar. Interestingly, in the Winchester edition, the boar was originally a bear, which could have been a potential political remark on the part of the author in reference to the War of the Roses.

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In Book 15, Launcelot prayed at a cross for his sins to be forgiven. He soon fell asleep and dreamed of a man with a gold crown, who was accompanied by seven kings and two knights. All worshipped at the foot of the cross, asking for God to visit them from heaven. Launcelot saw the clouds part, and an old man descend amongst angels to bless the supplicants. He chided one of the knights for disappointing him by fighting for "vain-glory."

The next day, Launcelot rode until he met a hermit. He told the hermit of his dream, and the hermit explained that Launcelot was a descendant of Joseph of Aramathie, and that his son Galahad was predestined to surpass all earthly knights, including Launcelot himself. The hermit told him to allow Galahad his own life, and that the sins of the father should not repeat themselves on the son, nor vice versa. Each should bear his own burden. Launcelot had supper with the hermit, and he suffered that night while he slept in his hair shirt. The next morning, he departed.