Illuminations (1968), by Walter Benjamin is a collection of essays from one of the most interesting and independent thinkers of theFrankfurt School. Especially apropos to "Beware of Ruins" is the essay "Theses on the Philosophy of History."

Michel Foucault's Language, Counter-Memory, Practice (1977), is a collection of essays, and interviews with the author. See especially, "Nietzsche, Genealogy, History."

A Primer of Freudian Psychology (1982) is a small introduction to Freud's thought and practice, of which memory and dreams comprise two indispensable constituents. Includes an index.

The Collected Poems of W. B. Yeats (1996) contains many poems of aging, memory and death. See especially "Sailing to Byzantium," and "A Prayer for Old Age."

"Gerontion" (1920) by T.S. Eliot is an excellent poem on aging.