Viharas were for the purpose of living, Chaityas were assemblies for the purpose of discussions. Further, Chaityas were with Stupas, Viharas did not have stupas.
Seven major pillar edicts have been found at Lauriya-Araraj, Lauriya Nandangarh, Rampurva, Nigali Sagar, Sarnath, Topra, and Meerut. Ashokan pillars probably signify the axis of the world (axis mundi) that separated heaven and earth.
EXAMIANS