Founded in the fifth century AD by the Guptas, the great monastic Buddhist university of Nalanda attracted thousands of international students and teachers until it was sacked by the Afghan invader Bhaktiar Khilji in the twelfth century. Courses included philosophy, logic, theology, grammar, astronomy, mathematics and medicine. Excavations have revealed nine levels of occupation on the site, dating back to the time of the Buddha and Mahavira in the sixth century BC. The site is strewn with the remains of stupas, temples and eleven monasteries, their thick walls impressively intact. Nalanda is now part of the modern Buddhist pilgrimage circuit, but even casual tourists will appreciate taking the time to walk through the extensive site, or climb its massive 31m stupa for commanding views. Informative booklets available at the ticket booth render the numerous guides unnecessary. Nalanda Museum houses antiquities found here and at Rajgir, including Buddhist and Hindu bronzes and a number of undamaged statues of the Buddha.