The technological advancement (in terms of art & architecture as well as science & technology) of Satavahana period was pretty advanced. Art and Architecture Taxila, Sakala, Bhita, Kausambi, Ahichchhatra, Patliputra, Nagrujunkonda, Amaravati, Kaveripattanam were well planned and developed cities, protected by fortification walls and moats. Buddhism stupas at Sanchi, Amaravati, Bharhut, and Sarnath are the best examples of art and architecture that flourished during this period. Stupa is a hemispherical dome or mound built over sacred relics either of the Buddha himself or of a sanctified monk or a sacred text. Buddha relics were kept in a casket in a smaller chamber in the center of the base of the stupa. The stupa has a fenced path around called ‘Pradakshinapatha.’ The four gateways of Sanchi stupa built in the first century B.C. are extremely artistic and are one of the finest examples of art and architecture of India. One of these gateways was donated by the Guild of ivory workers of Vidisa. Rock-cut caves are another form of marvel architecture of this period. These rock-cut caves are of two types, namely − A stupa and worshipping hall called as ‘Chaitya’ and Monastery called as ‘Vihara.’