Saiva Siddhanta is the oldest, most vigorous and extensively practiced Saivite Hindu school today, encompassing millions of devotees, thousands of active temples and dozens of living monastic and ascetic traditions. Despite its popularity, Siddhanta's glorious past as an all-India denomination is relatively unknown and it is identified today primarily with its South Indian, Tamil form. The term Saiva Siddhanta means "the final or established conclusions of Saivism." It is the formalized theology of the divine revelations contained in the twenty-eight Saiva Agamas. The first known guru of the Shuddha, "pure," Saiva Siddhanta tradition was Maharishi Nandinatha of Kashmir (ca 250 bce), recorded in Panini's book of grammar as the teacher of rishis Patanjali, Vyaghrapada and Vasishtha. The only surviving written work of Maharishi Nandinatha are twenty-six Sanskrit verses, called the Nandikeshvara Kashika, in which he carried forward the ancient teachings. Because of his monistic approach, Nandinatha is often considered by scholars as an exponent of the Advaita school. The next prominent guru on record is Rishi Tirumular, a siddha in the line of Nandinatha who came from the Valley of Kashmir to South India to propound the sacred teachings of the twenty-eight Saiva Agamas. In his profound work the Tirumantiram, "Holy Incantation," Tirumular for the first time put the vast writings of the Agamas and the Shuddha Siddhanta philosophy into the sweet Tamil language. Rishi Tirumular, like his satguru, Maharishi Nandinatha, propounds a monistic theism in which Siva is both material and efficient cause, immanent and transcendent. Siva creates souls and world through emanation from Himself, ultimately reabsorbing them in His oceanic Being, as water flows into water, fire into fire, ether into ether. The Tirumantiram unfolds the way of Siddhanta as a progressive, four-fold path of charya, virtuous and moral living; kriya, temple worship; and yoga-internalized worship and union with Parasiva through the grace of the living satguru-which leads to the state of jnana and liberation. After liberation, the soul body continues to evolve until it fully merges with God-jiva becomes Siva. Tirumular's Shuddha Saiva Siddhanta shares common distant roots with Mahasiddhayogi Gorakshanatha's Siddha Siddhanta in that both are Natha teaching lineages. Tirumular's lineage is known as the Nandinatha Sampradaya, Gorakshanatha's is called the adinatha Sampradaya. Saiva Siddhanta flowered in South India as a forceful bhakti movement infused with insights on siddha yoga. During the seventh to ninth centuries, saints Sambandar, Appar and Sundarar pilgrimaged from temple to temple, singing soulfully of Siva's greatness. They were instrumental in successfully defending Saivism against the threats of Buddhism and Jainism. Soon thereafter, a king's Prime Minister, Manikkavasagar, renounced a world of wealth and fame to seek and serve God. His heart-melting verses, called Tiruvacagam, are full of visionary experience, divine love and urgent striving for Truth. The songs of these four saints are part of the compendium known as Tirumurai, which along with the Vedas and Saiva Agamas form the scriptural basis of Saiva Siddhanta in Tamil Nadu. Besides the saints, philosophers and ascetics, there were innumerable siddhas, "accomplished ones," God-intoxicated men who roamed their way through the centuries as saints, gurus, inspired devotees or even despised outcastes. Saiva Siddhanta makes a special claim on them, but their presence and revelation cut across all schools, philosophies and lineages to keep the true spirit of Siva present on earth. These siddhas provided the central source of power to spur the religion from age to age. The well-known names include Sage Agastya, Bhoga Rishi, Tirumular and Gorakshanatha. They are revered by the Siddha Siddhantins, Kashmir Saivites and even by the Nepalese branches of Buddhism. In Central India, Saiva Siddhanta of the Sanskrit tradition was first institutionalized by Guhavasi Siddha (ca 675). The third successor in his line, Rudrashambhu, also known as Amardaka Tirthanatha, founded the amardaka monastic order (ca 775) in Andhra Pradesh. From this time, three monastic orders arose that were instrumental in Saiva Siddhanta's diffusion throughout India. Along with the Amardaka order (which identified with one of Saivism's holiest cities, Ujjain) were the Mattamayura Order, in the capital of the Chalukya dynasty, near the Punjab, and the Madhumateya order of Central India. Each of these developed numerous sub-orders, as the Siddhanta monastics, full of missionary spirit, used the influence of their royal patrons to propagate the teachings in neighboring kingdoms, particularly in South India. From Mattamayura, they established monasteries in Maharashtra, Karnataka, Andhra and Kerala (ca 800). Of the many gurus and acharyas that followed, spreading Siddhanta through the whole of India, two siddhas, Sadyojyoti and Brihaspati of Central India (ca 850), are credited with the systematization of the theology in Sanskrit. Sadyojyoti, initiated by the Kashmir guru Ugrajyoti, propounded the Siddhanta philosophical views as found in the Raurava Agama. He was succeeded by Ramakantha I, Shrikantha, Narayanakantha and Ramakantha II, each of whom wrote numerous treatises on Saiva Siddhanta. Later, King Bhoja Paramara of Gujarat (ca 1018) condensed the massive body of Siddhanta scriptural texts that preceded him into a one concise metaphysical treatise called Tattva Prakasha, considered a foremost Sanskrit scripture on Saiva Siddhanta. Affirming the monistic view of Saiva Siddhanta was Shrikumara (ca 1056), stating in his commentary, Tatparyadipika, on Bhoja Paramara's works, that Pati, pashu and pasha are ultimately one, and that revelation declares that Siva is one. He is the essence of everything. Shrikumara maintained that Siva is both the efficient and the material cause of the universe. Saiva Siddhanta was readily accepted wherever it spread in India and continued to blossom until the Islamic invasions, which virtually annihilated all traces of Siddhanta from North and Central India, limiting its open practice to the southern areas of the subcontinent. It was in the twelfth century that Aghorasiva took up the task of amalgamating the Sanskrit Siddhanta tradition of the North with the Southern, Tamil Siddhanta. As the head of a branch monastery of the amardaka Order in Chidambaram, Aghorasiva gave a unique slant to Saiva Siddhanta theology, paving the way for a new pluralistic school. In strongly refuting any monist interpretations of Siddhanta, Aghorasiva brought a dramatic change in the understanding of the Godhead by classifying the first five principles, or tattvas (Nada, Bindu, Sadasiva, Ishvara and Shuddhavidya), into the category of pasha (bonds), stating they were effects of a cause and inherently unconscious substances. This was clearly a departure from the traditional teaching in which these five were part of the divine nature of God. Aghorasiva thus inaugurated a new Siddhanta, divergent from the original monistic Saiva Siddhanta of the Himalayas. Despite Aghorasiva's pluralistic viewpoint of Siddhanta, he was successful in preserving the invaluable Sanskritic rituals of the ancient Agamic tradition through his writings. To this day, Aghorasiva's Siddhanta philosophy is followed by almost all of the hereditary Sivacharya temple priests, and his Paddhati texts on the Agamas have become the standard puja manuals. His Kriyakramadyotika is a vast work covering nearly all aspects of Saiva Siddhanta ritual, including diksha, samskaras, atmartha puja and installation of Deities. In the thirteenth century, another important development occurred in Saiva Siddhanta when Meykandar wrote the twelve-verse Sivajnanabodham. This and subsequent works by other writers laid the foundation of the Meykandar Sampradaya, which propounds a pluralistic realism wherein God, souls and world are coexistent and without beginning. Siva is efficient but not material cause. They view the soul's merging in Siva as salt in water, an eternal oneness that is also twoness. This school's literature has so dominated scholarship that Saiva Siddhanta is often erroneously identified as exclusively pluralistic. In truth, there are two interpretations, one monistic and another dualistic, of which the former is the original philosophical premise found in pre-Meykandar scriptures, including the Upanishads. Saiva Siddhanta is rich in its temple traditions, religious festivals, sacred arts, spiritual culture, priestly clans, monastic orders and guru-disciple lineages. All these still thrive. Today Saiva Siddhanta is most prominent among sixty million Tamil Saivites who live mostly in South India and Sri Lanka. Here and elsewhere in the world, prominent Siddhanta societies, temples and monasteries abound.