Achievment of Kanishka bought the spreading of Buddhism after Ashokan period. Kanishka, the famous king of the Kushana dynasty, was born of mixed race. But he became an Indian because of his long acquaintance with the people and culture of the land. Kanishka transformed into a devoted Buddhist during the course of his reign. The coins of Kanishka pointed to the gradual alteration of his religious beliefs initiated with pantheism and culminating in adoption of Buddhism. There are various legends depicting the story of Kanishka's conversion.

Religious Policy of Kanishka
Historians therefore depend on the legends to determine the religious policy of Kanishka. According to such a legend, the influence of the great scholar Asvaghosa led to the conversion of Kanishka. After occupying Pataliputra, Kanishka came in contact with Asvaghosa. Kanishka was very much impressed with the teachings of Asvaghosa. Asvaghosa accompanied him to Peshawar and introduced him to the Buddhist creed. Though a dedicated Buddhist himself, Kanishka was not a bigot. He was equally tolerant towards the other religious creeds, which are evident from the figures of various Hindu, Persian and Greek deities, found on his coins. Some scholars however suggests that these figures are not conclusive proofs of the religious toleration of Kanishka, rather the coins can be considered merely a token, which indicates the diversity of religious beliefs and ideas within his Empire.

The reign of Kanishka left a memorable mark in the history of ancient India, particularly for his patronage to the religion of Sakyamuni. Ashoka devoted his life for the spread of the Hinyana creed while Kanishka devoted himself to the service of the Mahayana creed. Different scholars have approached different theories regarding the actual date of Kanishka's conversion into Buddhism. Some scholars are of the view that Kanishka embraced Buddhism during the first era of his reign. Sten Konow had come to this conclusion after reading a date in the Peshawar casket information. According to Konow the date denotes the first year of Kanishka's reign. But B.N Mukherjee has suggested that the Peshawar casket information did not bear any date. However it is generally believed that Kanishka embraced Buddhism after his invasion of Pataliputra, where he came under the influence of the Buddhist scholar Asvaghosa.

Fourt Buddhist Council in Kanishka's time
During Kanishka, the famous Fourth Buddhist council was convoked at Kundalavana Vihara. Though there are enough controversies among the scholars about the actual location of Kundalavana Vihara, it is generally believed that Kundalavana Vihara was located in Kashmir. A selected body of scholars participated in the council. The fourth Buddhist council was organised under the patronage of Kanishka, which was headed by scholars like Vasumitra and Asvaghosa.

The Convocation of the first Buddhist council marked the ascendancy of the Mahayana Buddhism with Sanskrit as its vehicle of propagation. Kanishka regarded Mahayana as his state religion. The state religion of Kanishka determined preaching the divinity of Gautama Buddha and the worship of Buddha's image had a greater appeal compared to the dry, scholastic Hinyana creed. Mahayanism, the state religion of Kanishka preached not only the divinity of Buddha and the worship of the Buddha image, but it also preached the efficacy of prayer, devotion and faith. Salvation of entire universe was the ideal of Mahayanism. Moreover the medium of propagation of Buddhism was Sanskrit, which had some social significance. Kanishka undertook this step because at that time Sanskrit was considered an aristocratic language, which was ornamental and literary than the spoken language Pali. Therefore with the use of Sanskrit as the medium of propagation, Kanishka intended to alienate Buddhism from the common masses. Kanishka in his religious policy of Mahayanism discarded the doctrine of personal salvation by penance and ethical practices in order to be "self illuminated". The religious policy of Kanishka stated that Bodhisatva would work for the salvation of all beings. Hence during the reign of Kanishka, people did not need to undergo hardship and penance in order to attain salvation. Kanishka replaced the worship of Buddhist Symbols like Buddha's footprints, Dharmachakra, stupa or Bodhi Tree by initiating the worship of Buddha and Bodhisattva images.

Buddhism in Kanishka's time
The cult of Bodhisattva and the worship of Buddha images became widely prevalent in the Kushana period. One of the earliest figures of Buddha are found in Kanishka's coins and in the Peshawar casket. The term "Bodhisattva" had a dual significance as it was upheld by the religious policy initiated by Kanishka. In one sense it meant a person worked for the salvation of the mankind. In the second sense it meant the previous incarnation of Buddha. Kanishka also undertook the policy of propagating his religion to the distant countries including Tibet, China, Burma and Japan. Historians have later presumed that since Kanishka had commanded over the major parts of Central Asia, his own creed of Mahayanism was spread to those countries. From the accounts of Hiuen Tsang and Al Beruni, it is known that Kanishka constructed the great relic tower at Peshawar, which was famous throughout the Buddhist world. The Greek architect Agelisas or Agisala constructed the tower. Mahayana Buddhism, as the state religion of the Kushanas received a great impetus.

Kanishka's reign as Indian Renaissance
Kanishka's reign as figured the Indian Renaissance, which had its full development in the Gupta Age. Historians have opined that the Kushana age was the introduction to the Gupta Civilisation. Sanskrit was restored with a former glory after it had disappeared in obscurity after the Mauryas. Kanishka gave his royal patronage to the language. All the Mahayana scriptures were written in Sanskrit language. Galaxies of great scholars like Asvaghosa (the Buddhist Writer), Nagarjuna (the philosopher), Samgharaksha (the chaplain), Mathara (the politician), Vasumitra (the Buddhist scholar), Charaka (the physician) and Agisala (the engineer) adorned the court of Kanishka. Asvaghosa was not only a great philosopher but also a great poet and author of the famous epic 'Buddha Charita'. Asvaghosa also wrote "Sundarananda Kavya", which deals with the episodes of Buddha's life. Asvaghosa at the same time wrote several philosophical treatises, which were of immense importance. "Sutralankara" was another important work composed by a scholar named Kumaralata in Taxila. Matricheta was another contemporary, who composed Buddhist hymns or Stotras, which were very popular in Central Asia and Tibet. Nagarjuna was a competent exponent of Mahayana philosophy. Learning and literature were augmented due to the patronage of the Kushana king Kanishka.

Art and architecture under Kanishka
Kanishka's reign was a landmark in the realm of art and architecture. Four eminent schools of art received great impetus during his reign. These were Sarnath, Mathura, Amaravati and Gandhara. Among the four schools, the Gandhara School of Art received a thriving prosperity during the reign of Kanishka. In art, Kanishka's reign was marked with the growth of two distinct styles, one Indian and another exotic. The Indian style was represented by the headless statue of Kanishka at Mathura and the image of Buddha found at Sarnath. The exotic school known as Gandhara art was Graoko-Roman art applied to the Buddhist subjects found in Gandhara Region. In the field of architecture too Kanishka's reign was highly creative. Numerous stupas, monuments, columns were built during his sovereignty.

In short, during the rule of Kanishka, India reached culmination in the fields of art, architecture, learning and literature