What are the stories about swallows on the murals?

Swallow is like a hopeful spring in a year, so it is a symbol of good luck. Yan is a migratory bird, which migrates with the change of seasons and likes to enter and leave people's houses or eaves in pairs. Therefore, it is favored by the ancients and often appears in ancient poetry, or cherishes spring and hurts autumn, or exaggerates sadness, or reposes lovesickness, or is sentimental about current events, with rich images and expressive expressions, which are far behind other things.