In the west, we tend to think that philosophy began in Greece with Socrates, Plato, Aristotle and others, or earlier thinkers like Thales and Pythagoras. Around 500 BC Pythagoras practiced the love of wisdom, or philosophy, and at the same time, there were many religious philosophies in China like Confucianism and Taoism, Zoroastrianism in the Middle East with its dualistic cosmology of good and evil, and elsewhere.
The Avesta is the key scripture of Zoroastrianism, which begun around 1,500 BC. Written in the Avestan Language, which is similar to Sanskrit, which was in use in India by 3,000 BC, and as long as the languages have existed, a body of religious philosophy has existed. The Rigveda is in Sanskrit and the oldest spiritual text in existence. The philosophy is of the Oral Tradition, which has existed as long as people have existed, but written down when writing developed around 3,000 BC.
The Sacred Text uses many names for the philosophy it advances such as the Middle Way, the way, the good path to good fortune, the Philosophical System of AH, the Doctrine of the Absolute Unity of Spirit, and so on. The school has yet to find where the philosophy appears in a structured way, maybe because it is not so complex. Anyway, here is what I have on the site about The Five Principles of the Philosophical System of AH.
Every living being is given the breath of life to enjoy the beauty and wonder of the earth or not, but if you do not master the system and have moral impurity you will experience life after life wondering here, in this place, no wonder it is called the hereafter. Living upon the earth can be difficult and dangerous, but to abandon the world to become a Buddha to come to enjoy freedom from suffering.
A Buddha is the highest state a human can attain and the enlightened of the world attain many other names as well such as Rishi, Angira, Aditya, Serpent King, Magi, Messiah, Shining One, and so on. Their teaching was, is, and will be the Philosophical System of AH. In ancient times, when the philosophy was understood and mastered countless Shining Ones walked the earth in service to humanity on any given day. The Holy Mantras say thousands have won the race with yama, death, and since the philosophy disappeared, zero. Here is a mantra from the Veda.
A cover in comparison is collected into a heap, empty, but connected to people with the air for filling a form. To bind to AH with competence to be present to reach to the suffering, and love for those in confusion is the Philosophical System of AH.