In the sacred land of Bharata, the wise sages have long taught of the four great ages through which the world passes: Kṛta, Tretā, Dvāpara, and Kali. These four yugas, or ages, unfold in a fixed sequence—first comes the Kṛta Yuga, followed by Tretā, then Dvāpara, and finally Kali, the age in which we now live. The sages explain that the Kṛta Yuga endures for four thousand years, with a dawn and a dusk—periods of transition—each as long as the age itself. For the three yugas that follow, their durations, including dawns and dusks, decrease by a quarter with each successive age. Those skilled in the reckoning of time declare that the Tretā Yuga lasts for three thousand years, with a twilight period of three hundred years at both its beginning and end. The Dvāpara Yuga is two thousand years long, with four hundred years as its dawn and dusk, while the Kali Yuga is said to last for one thousand years, with two hundred years as its twilight. All together, these four yugas—Kṛta, Tretā, Dvāpara, and Kali—comprise a cycle of twelve thousand years. But when measured in human years, the numbers grow vast. The Kṛta Yuga encompasses twenty-eight thousand human years; the Tretā Yuga, ninety-six thousand; the Dvāpara Yuga, sixty-four thousand; and the Kali Yuga, thirty-two thousand human years. Thus, the full cycle of four yugas, with their twilight periods, is reckoned by humans in this way. Seventy-one such cycles of four yugas, joined together, are known as a Manvantara. In human reckoning, the duration of a Manvantara is counted by the twice-born as thirty-one kotis, plus one hundred thousand, thirty-two thousand, eight hundred, and eighty years, with six additional months. The sages also speak of the interval between Manus, the progenitors of mankind, as one hundred thousand years by divine measure. The duration of a Manvantara is forty thousand years, including the yugas, according to the divine reckoning. Thus, seventy-one cycles of the four yugas complete a Manvantara. Fourteen such Manvantaras make a kalpa, and when these are complete, the great dissolution, or pralaya, occurs. The measure of a kalpa is twice as much as previously described, and the cycles of the yugas—Kṛta, Tretā, Dvāpara, and Kali—have thus been explained. Now, let us understand how the Tretā, Dvāpara, and Kali Yugas are created. Since Dvāpara and Kali arise together, their stories cannot be told separately. The narrative of these yugas has come in due order, and for two yugas, the rest was not told, as the sages were engaged in recounting the lineages of the rishis. What was left untold in the Tretā Yuga, I will now reveal. At the dawn of the Tretā Yuga, prompted by Brahmā, Manu and the seven great sages declared the dharma—both that which is found in the Vedas and that which is handed down by tradition. The seven sages proclaimed the śrauta dharma, rich with rituals concerning marriage, the sacred fire, and the collections of the Ṛg, Yajur, and Sāma Vedas. Manu Svāyambhuva, on the other hand, established the traditional dharma, grounded in right conduct and handed down through generations, joined with the practices of varṇa (social order) and āśrama (stages of life). Through truthfulness, celibacy, study, and austerity, and by the intense penance of the sages, dharma was preserved and passed on in proper succession. At the beginning of the Tretā Yuga, from Manu and the seven sages, the Vedic mantras—sometimes unintentionally, sometimes intentionally—began to flourish. These mantras, such as Tāraka and others, increased through divine visions and, in the first kalpa, appeared spontaneously among the gods. Among the authorities, among the perfected beings and others, the practice of mantra-yoga spread. In past kalpas, thousands of mantras appeared, and again they manifest in their forms. The mantras of the Ṛg, Yajus, Sāman, and Atharvan Vedas, as well as those taught by the seven sages, were preserved, while Manu declared the traditional dharma. At the beginning of the Tretā Yuga, the Vedas were united as the sole foundation of dharma. Yet, as human lifespans shortened, in the Dvāpara Yuga, the Vedas were divided. The sages, through great austerity, studied the Vedas day and night. These divine Vedas, without beginning or end, were revealed by Svayambhū (the self-born), complete with all their limbs, and established in their own dharma. In each yuga, the Vedas and their teachings adapt according to the dharma appropriate for that age. The initiation sacrifice (dikṣā) was prescribed for the kṣatriyas; the havis-sacrifices for the vaiśyas; service-sacrifices for the śūdras; and recitation-sacrifices for the brāhmaṇas. Thus, in the Tretā Yuga, the four varṇas arose, upholding dharma, performing their respective rites, bearing children, prospering, and living in happiness. Brāhmaṇas were established by brāhmaṇas, kṣatriyas by kṣatriyas, vaiśyas by vaiśyas, and śūdras followed, each supporting the others. Their natures were auspicious, and their dharmas were founded on the principles of varṇa and āśrama. In the Tretā Yuga, through intention, speech, and action, the performance of karma was unbroken and successful. Long life, good form, strength, intelligence, health, and righteousness were the common qualities of all in the Tretā Yuga. Brahmā himself established the system of varṇa and āśrama, along with the collections of mantras, health, and righteousness. The collections and mantras were given by the sages, the sons of Brahmā, and the sacrifice was established by the gods themselves. Thus, the progression of time, the order of the yugas, the establishment of dharma, and the practices of the varṇas and sages were set forth in the land of Bharata, ensuring the preservation of righteousness and the welfare of all beings.