Swallows nest in the bell and drum tower. Take a closer look: the bell and drum tower made a swallow-proof net for this purpose. Every morning and evening, thousands of swallows hover over the bell tower and drum tower in Xi 'an, which is very spectacular (above). This two thousand-year-old Gu Lou was also enlivened by the swallow. With the improvement of the environment in recent years, the population of swallows has been expanding, which has begun to affect the protection of two national key cultural relics, the Bell and Drum Tower. The depository has tried to set up an iron net to block the nesting and habitat of swallows, but the effect is very small (below). According to an expert on ancient architecture, the number of bell and drum towers inhabited by swallows has increased year after year because there are fewer and fewer civil buildings suitable for swallows to nest in Xi 'an, and ancient buildings such as bell and drum towers have become the only ideal homes for swallows. From the perspective of pure cultural relics protection, swallows' droppings and bird's nest are absolutely not allowed to pollute the paintings on ancient buildings. However, swallows are wild animals and need protection just like ancient buildings. Can they blend in and live in peace? After years of observation, experts believe that swallows can inhabit the Bell and Drum Tower. Cultural relics protection should be a complex. Swallows will not cause much damage to ancient buildings, but the number should be controlled in moderation, and the purpose of pulling nets is also here.