The Ancients including, but not limited to, the Ancient Greeks by virtue of having their thoughts and writings survive, serve for as as an early source of esoteric philosophy. Similarly, the Old Testament and it's hidden wisdom (the Qabalah), the Gnostic Christian and non Christian writings, and Babylonian Mythology remain cornerstones and the roots of modern esoteric thought.
Socrates (469 BCE – 399 BCE 469) teaches Plato, who teaches Aristotle (@ 424/423 BCE – 348/347 BCE ) who teaches Alexander the Great as a youth for his father, Philip II of Macedona. Alexander conquers the known world, founding his namesake city in Egypt, but populating it with Greeks and Macedonians. Once conquered, Alexander would put one of his Generals in charge as Governor, and encouraged them to adopt the titles, dress, customs and women of their new Kingdoms. His idea was to create a series of Kingdoms, each with an individual identity, but all beholden to Greek culture and political control.
When Alexander dies, most of his Generals return to their old wives and customs, but retain the titles they took upon becoming ruler of their new lands. In Egypt, General Claudius Ptolemy founds the Ptolemaic Kingdom, destined to later become the Byzantine Empire. While there were @ 20 cities named after Alexander, the Alexandria-by-Egypt housed a world famous Library and attracted scholars from across the ancient world. Founded by Ptolemy I Soter (323–283 BC) and his son Ptolemy II (283–246 BC), it was organized by Demetrius of Phaleron, a student of Aristotle. According to Plutarch (AD 46–120) Julius Caesar accidentally burned the library down in 48 BC, but a smaller library, the Serapeum, preserved some of its greatest treasures.
These ancient texts, primarily in Greek, were translated into the languages native to the Egyptian area, and resurfaced in Arabic and other languages when Islam made it's conquests of Africa and Spain.
There, a curious period of religious tolerance took hold between Muslims, Catholics and Jews, and from @ 1450 -1492 priests, rabbis and Imans discussed and shared their perspectives on God, the world and Man. This ended with the expulsion of the Jews in 1492 by Queen Isabella and King Ferdinand. Within another decades, they drove the Muslims out of Spain as well and invited the Inquisition in to harass any remaining non Christians.
But Greek learning had been returned to Europe, and the effect it had on the Scholasticism method of learning of the day was overwhelming. Philosophy courses today usually start with Socrates' method of questions, Plato's concept of Ideal Forms and Aristotle's syllogisms. The different approaches of Plato's deductive style and Aristotle's induction will be played out again in the 1700s between René Descartes (I think, therefore I am) and John Stuart Mills (everything we know, we know by our senses).
In these lay the foundation of Western Philosophy and Magick. In particular, Plato's belief that all physically perceivable object is a "shadow" or reflection of a spiritual FORM or Ideal is the basis of Sympathetic Magick, where the manipulation of a symbol or object connects to greater forces through it's active conduit of another. The sacrifice of corn for better harvests, the use of voodoo dolls, and the creation of Talismans all flow from this premise.
It is not a surprise, therefore, that the next group of esoteric philosophers emerge after these Greek works are translated into European languages and are called NeoPlatonists, in deference to Plato. The story continues on the Specialty Page, Neoplatonism.
Some of the other Philosophers who make up the Ancients are: Euclid of Alexandria; Democritus; Cicero, whose Memory Palace technique is crucial in Western Occult development; and Pythagoras, whose Mystery School was equally important as his Geometry.
also my own essay 3 Gnostic Rabbis exploration of the Gnostic Neoplatonism of the Ancients aka Gnostic Qabalah;