Lime is an ancient construction material that has been utilized throughout the world in various forms, providing stable construction methods in usable conditions. Lime mortar is well known for its low carbon footprint in production and carbon absorption throughout its lifespan as a hardened material. The significant benefits of lime mortar were analyzed and reviewed for further research. Ancient lime constructions need proper maintenance for aesthetic and structural strengthening to preserve this cultural architecture of national pride. Hence, the characterization of ancient mortars is mandatory for renovation work. Here, we studied the various characterization methods available worldwide. We analyzed samples taken from the 1900-year-old Vedapureeswarar Temple of Thiruvothur, Cheyyar, and the 1800-year-old Lakshmi Narasimhar Temple of Parikkal, located in Tamil Nadu. Hardened samples from these two ancient temples were collected and analyzed. The mineralogical characterization of these mortars using SEM, XRF, FTIR and XRD gave immense knowledge of the mortar matrix. Experimental analysis indicated that using natural organic materials in the lime has made the structures more potent and stable. The characterization study provided information on the ratio of mortar mix used, the presence of organic ingredients, and the need for compatible repair materials for proper maintenance of the temple structures. The characterization study furthers the necessary knowledge to provide a compatible repair material and indicates the need for ancient construction technology in the current highly polluted environment.