Tepe Rustam is a mound located to the south of the modern city of Balkh, some 700 meters south of the medieval city wall, containing the ruins of a stupa. Some scholars believe this to be the remains of the shrine associated with the monastery of Naw Bahar described by a Chinese pilgrim who visited the site in the seventh century CE. The nearby ruin known as Takht-i Rustam has been tentatively identified as a monastery. Whatever its identity, it was one of the largest stupas north of the Indian subcontinent and must have been a grand building, indeed. 

Sources:

X. de Planhol, C. E. Bosworth, V. Fourniau, D. Balland, F. Grenet. "BALḴ." Encyclopaedia Iranica, Vol. III, Fasc. 6 (London, 1989), 587-596. Available online at http://www.iranicaonline.org/articles/balk-town-and-province (accessed March 19, 2020).