In 1954, Rothbard, along with several other attendees of Mises' seminar, joined the circle of Novelist Ayn Rand, the founder of Objectivism. He soon parted from her, writing, among other things, that her ideas were not as original as she proclaimed but similar to those of Aristotle, Thomas Aquinas and Herbert Spencer. In 1958, however, after the publication of Rand's novel, Atlas Shrugged, Rothbard wrote a "fan letter" to her, calling the book "an infinite treasure house," and "not merely the greatest novel ever written, [but] one of the very greatest books ever written, fiction or nonfiction." He also wrote, "you introduced me to the whole field of natural rights and natural law philosophy," prompting him to learn "the glorious natural rights tradition." Rothbard rejoined Rand's circle for a few months, but soon broke with Rand once more, over various differences, including his defense of anarchism.