During the structural restoration of an abandoned 9th-century Sun Temple in Rajasthan's Alwar district, conservationists discovered a unique optical feature embedded in the sandstone architecture. Hidden within the southern and northern vents of the sanctum, a series of polished rock-crystal lenses were found, designed to concentrate and project sunlight directly onto the central Surya idol during the equinoxes.
This "Solar-Lens" system demonstrates an advanced understanding of dioptrics and astronomical alignment by medieval Indian architects. The restoration project, led by the Archaeological Survey of India (ASI), aims to stabilize the deteriorating sandstone carvings while preserving the functional integrity of this ancient light-harvesting mechanism, which had been obscured by centuries of soot and debris.