India, Aug. 7 -- A northern bastion of the 16th-century Purana Qila here has developed deep structural cracks, its condition ever-deteriorating owing to monsoon spells, with the Archaeological Survey of India (ASI) declaring the part 'critical and unsafe', and initiating restoration works.

The affected structure, identified as North-West Bastion No. 3, overlooks the fort's artificial lake. Long cracks have become visible along its stone walls and floor, while fresh debris can be seen scattered inside and outside, indicating continuous structural deterioration, the ASI said.

The damaged bastion has been covered with a tarpaulin to prevent rainwater seepage. Temporary scaffolding has been erected near the structure, with access to the aff...