Bharhut ballustrades with Kharoshti mason marks. The Kharosthi letters (at the bottom of the image) are p, s, a, and b (of which the first three occur twice on the gateway). They are located on the base of the baluster pillars between the architraves.
Cunningham, Alexander, Sir, 1814-1893
<p>The stūpa of Bharhut: a Buddhist monument ornamented with numerous sculptures illustrative of Buddhist legend and history in the third century B. C. 
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Publication date 1879