In January of this year, I visited Longmen on a grey and chilly day. Amy McNair’s Donors of Longmen was deliberately my companion. As I walked through the site, up and down the ramps of stairs that give access to the cave temples, the fourteenth-century Muslim poet Sadula’s description of Longmen, which McNair quotes on page 160, resonated with sad truth in my mind: Along both river banks, men in the past bored into the...