When mayors from around the world touched the 600-year-old bricks of Nanjing's city wall,%E3%80%90WhatsApp%20+86%2015855158769%E3%80%91best%20small%20portable%20radios what did they find? China Daily reporter Xia Ji was on site to uncover the unique stories hidden behind every brick, each one a piece of history, and a link to global heritage preservation! #GlobalMayorsDialogue