Plotinus, born in Lycopolis, Egypt, when it was part of the Roman Empire, was a major figure in the philosophical school later called Neoplatonism. Neoplatonists viewed reality as deriving from a single force or figure expressed as 'the One'. Two further concepts from Plotinus, 'the Intellect' and 'the Soul', are also principal features of his philosophy. These proposals led to the work of Plotinus forming a bridge between Plato and the monotheistic religions of Christianity, Judaism and Islam as well as Gnosticism.

Being and Time was published in 1927 during the Weimar period in Germany, a time of political, social and economic turmoil. Heidegger himself did not escape the pressures and his nationalism, and undeniable anti-Semitism in the following decades cast a shadow over the man, but not the work. Being and Time is not coloured by expressions of his later views (unlike other writings) and remains an outstanding document.

Aristotle's Metaphysics was the first major study of the subject of metaphysics - in other words, an inquiry into 'first philosophy', or 'wisdom'. It differs from Physics which is concerned with the natural world: things which are subject to the laws of nature, things that move and change, are measurable. In Metaphysics, the study falls on 'being qua being' - being insofar as it is being; the causes and principles of being, the causes and principles of substances.

The Summa Theologica, by Thomas Aquinas, is a fundamental text in Catholic doctrine, a compendium of theology that has been studied and debated since its first publication in the 13th century. Furthermore, it has been widely regarded as one of the classics of Western philosophy, not least because, perhaps for the first time in such a systematic manner, it set out to consider the views of non-Christian figures such as Aristotle, Boethius, Muslim writers including Averroes (Ibn Rushd) and Avicenna (Ibn Sina) and the Sephardic Jewish scholar Maimonides.

Composed in four parts between 1883 and 1885, Thus Spoke Zarathustra is the most famous and influential work of German philosopher Friedrich Nietzsche. The work is a philosophical novel in which the character of Zarathustra, a religious prophet-like figure, delivers a series of lessons and sermons in a Biblical style that articulate the central ideas of Nietzsche's mature thought.