I just read that Mary Stewart died.
I must have read "The Crystal Cave," "The Hollow Hills," and "The Last Enchantment" ten times in the 1970's, and would return to them over the 80's. (Alas, I never much cared for her later work, "The Wicked Day.") The series was my introduction to pre-Christian Britain, and I wished that I could find a cave with a shrine to "Miridden" near our house (it would be years before I realized the proper pronunciation of Myrddin was "Mirthin").
What I remember liking most about the stories was how I identified with the boy Merlin, how Merlin's magic was a wonderful mixture of engineering and prophesy, how Merlin understood the psychology of his actions, and the historical underpinnings of England in the middle ages. I thought she handled the whole Arthur-Guinevere-Lancelot triangle well (although at that time I was more interested in the magic and intrigue than I was in mushy French romantic embroidery).
Her stories were the first books in what would eventually become the Arthuriana section of my library. I'll have to take them down, dust them off, and reread them again.