"Oxygen insulation is the best way to protect the ancient city wall and is conducive to the wall's 'longevity'," says Wang Su, a researcher at Xi'an Tang Imperial City Hanguang Gate Relics Museum.

Zhang Qingsan, a staff member of the Bell and Drum Towers Museum, who is responsible for the renovation project on the tower this year, says he and his colleagues will always stick to the ethos of "minimum intervention"－a basic principle in historic heritage restoration and protection－during the renovation, and will always try their best to keep the original look of the Bell Tower.

"After the restoration, the tower won't change much in the eyes of tourists," he says. "But from the perspective of relic protection, the 'life span' of the tower will be prolonged greatly."

Wang Lei says he's glad to find that so many people have noticed the changes to the Bell Tower. "Even before the renovation, some residents and tourists had already noticed the effects of weathering on the tower and made suggestions to us that the tower should be renovated," he says.

"We really appreciate people's affection for the Bell Tower and their sense for protecting it," Wang adds.

Wang Yiming, a resident in Xi'an's Beilin district, the site of the ancient city wall and the Bell Tower, says he passes the tower and sees the city wall almost every day.

"As part of our heritage, dating back hundreds of years, they do need regular restoration and protection to reduce damage by weathering, so that they can better show our culture and history to tourists from China and overseas," he says.