[3][4] In 1726, he constructed the steps which led to the Catholic shrine atop St Thomas Mount which still bears a slab commemorating Uscan's legacy.
In 1740, when the Raghuji Bhonsle of Nagpur invaded the Carnatic, Petrus Uscan was appointed the British envoy to negotiate peace with the Maratha general.
[2] Uscan negotiated with the Marathas and impressed the general so much that he even recognized British rule over Tiruchirappalli, Madras and Fort St David.
[2] On another occasion, Petrus Uscan succeeded in obtaining exclusive rights for the British of Madras to mint coins in their own name.
[5] When Madras reverted to British control in 1749, Petrus Uscan and one Mrs. Madeiros were the only Catholics permitted to reside in the Fort.
[5] Petrus managed to retain Armenian hold over the Chapel of Our Lady of Miracles in Vepery for some time.
[7] The community has almost become extinct, yet its memory survives through Petrus Uscan's numerous endowments and works of charity.