Conrad Joachim, a German immigrant, marched off to war from his home on Greenwich Street in Manhattan on May 13, 1862, enlisting as an assistant surgeon in the 15th New York Heavy Artillery. Charles Joachim, whom historians believe to be his son, had already joined the same unit.

Four months later, Conrad was dead; and in another year, so was Charles, at about the age of 20. They were buried in the same grave at Green-Wood Cemetery in Brooklyn, beneath a marble headstone that is an exquisitely carved open book inscribed with both their names. But the stone slowly sank into the earth as the centuries turned twice, and the cemetery and the city were completed around them.

The Joachim family’s sacrifice may have been forever lost to history if not for a formidable labor of detective work involving hundreds of volunteers and lasting longer than the Civil War itself. Now the Joachims are among more than 1,200 Civil War soldiers with new gravestones at Green-Wood. And today, for the first time, the cemetery is honoring the full known complement of veterans of the country’s deadliest war.