A Preventive Approach

To most visitors, the Fengxian Temple, the largest cliffside niche shrine at the Longmen Grottoes, is a great option for taking photos. To the researchers at the Longmen Grottoes Academy, it is a precious heritage to guard carefully, where every crack and damp patch is a symptom demanding immediate attention.

The temple houses the Vairocana Buddha, the tallest and most artistically accomplished statue at the site.

Water infiltration has been a persistent threat for over a millennium. Just above the southern slope of the temple sits a karst cave. Because limestone is highly soluble, water seeped through the stone, shaping the cave's stalactites and stalagmites over thousands of years. It also threatened the precious stone statues below.

Fan Zilong, who heads the Protection and Restoration Section at the Academy, said as early as the Tang Dynasty (618-907), ancient craftsmen dug drainage channels above the Fengxian Temple to prevent seepage from eroding the great Buddha. More than a thousand years later, this system is still functioning. "The ancient craftsmen's site-sensitive wisdom is an inseparable part of the cultural heritage itself," Fan said.

Yet managing water infiltration still remains one of the most difficult challenges in grotto conservation. The ancient channels could do only so much. What was needed was a way to detect problems before they became disasters.

That was where modern technology stepped in. Field inspections that used to take Fan and his peers two weeks can now be done sitting in front of a computer, reviewing real-time data from key monitoring points. "It is like taking a patient's blood pressure and checking their blood sugar and lipids," Fan said.

The monitoring system tracks three main dimensions, each marked in a different color on the dashboard: the atmospheric environment, the cave micro-environment, and the cultural relics themselves. Atmospheric monitoring tracks temperature, humidity, rainfall, and wind speed, while the cave micro-environment monitors internal temperature, humidity, and wall temperature. Together, they paint a complete picture of the grotto's "health."

The system proved its worth during the torrential rains that hit Luoyang in July 2021. "We were staring at the screens day and night, monitoring every change," recalled Liu Yi, a member of the team. Thanks to the early warning system, they noticed abnormal readings from crack displacement meters at the south cave of Leigutai, a group of three parallel caves and niches. "The data showed structural instability after the heavy rain. Without timely reinforcement, there was a real risk of collapse."

The team rushed to the site and installed emergency shoring, reinforcing the exterior with steel supports and adding bracing inside. And then came an unexpected reward. When they later dismantled the front wall, they discovered an 80-centimeter gap hiding more than 80 relic fragments. "The most exquisite piece was a Buddha head from the Tang Dynasty," Liu said. In responding to one emergency, they had uncovered a hidden treasure.

For Fan and Liu, however, the real significance of this work lies not in any single discovery, but in a fundamental shift in conservation philosophy —from reactive, emergency interventions to preventive care. The monitoring platform is not just a tool; it is a new way of thinking about stewardship.

"Just as people today pay attention to their health and get regular checkups, monitoring allows us to detect problems early and intervene before they get worse," Liu remarked.

In the end, the true guardians of Longmen are not the sensors or the screens. They are the vigilant minds behind them. Their goal is not simply to repair the past, but to safeguard it for the future.

Source: Science and Technology Daily