Definition of "deas"

I could never think of a King but what I supposed him sitting under the high deas, and feasting amid his high vassals and Paladins, eating blanc-manger, with a great gold crown upon his head, or else charging at the head of his troops like Charlemagne in the romaunts, or like Robert Bruce or William Wallace in our own true histories.

1823, [Walter Scott], “The Man-at-Arms”, in Quentin Durward. […], volume I, Edinburgh: […] [James Ballantyne and Co.] for Archibald Constable and Co.; London: Hurst, Robinson, and Co., page 109