Short answers, pulled from the story.
Gandharan Buddhism began around the 3rd century BCE when the Mauryan emperor Ashoka sent missionaries to the region following the Third Buddhist Council in Pataliputra. It continued until approximately 1200 CE, when Buddhism ceased to exist as a living tradition in the region due to a combination of invasions and other factors.
The Gandharan Buddhist texts are the oldest Buddhist manuscripts ever discovered, dating to approximately the 1st century CE. Written in the Gandhari language using the Kharosthi script on birchbark and palm leaf, they cover genres including prose sutras, poetry, Abhidharma, Vinaya, and Mahayana texts. Scholar Richard Salomon attributed most of them to the Dharmaguptaka school.
Greco-Roman artistic culture led Gandharan sculptors to create the first anthropomorphic depictions of the Buddha, representing him in human form rather than through symbols. The resulting style blended Indian, Hellenistic, Roman, and Parthian elements, visible in the drapery and hairstyle of Gandharan Buddha figures. This fusion reached its height during the Kushan Empire period from 30 to 375 CE.
Kanishka the Great, who ruled from 128 to 151 CE, built Buddhist stupas and monasteries in Peshawar, the Kushan capital. His patronage helped produce the architectural flowering whose remains, including sites like Takht-i-Bahi, Sahri-Bahlol, and Taxila, form the bulk of Gandharan Buddhist architecture that survives today.
Gandharan missionaries traveled through the Khyber Pass and along the Silk Road through the oasis towns of the Tarim Basin, including Khotan and Turpan, reaching China during the Han dynasty from 202 BCE to 220 CE. Key translators included Lokakshema and An Shigao in the 2nd century, Dharmaraksha from 265 to 313, and Danapala during the Song dynasty in the 11th century.
The Hephthalite White Huns invaded Gandhara around the middle of the 5th century, dealing a severe blow to Buddhist institutions. After Hephthalite rule ended in the 6th century, sites continued to decline. Muslim invasions later caused further damage, and Buddhism had ceased to exist in the region by approximately 1200 CE.