A cenotaph is a monument built to honor people whose remains are interred elsewhere or whose remains cannot be recovered. The Cenotaph in London was originally built to honor the dead of World War I, but it now honors all dead British service members from all wars.
What's a cenotaph? Every Veterans Day, I hear about the Queen of England laying a wreath at the Cenotaph in London.
Cenotaphs memorialize the non-military, as well. In Nicholas Sparks' memoir, Three Weeks with My Brother, he describes the Taj Mahal in India:
The Taj Mahal was begun in 1631 by Shah Jahan, a Mughal emperor, in memory of his second wife, Mumtaz Mahal, who died after giving birth to their fourteenth child. . . . The cenotaph honoring Mumtaz Mahal inside the Taj is inlaid with jewels and lies near that of her husband's.