Toby Angel first became aware of barrows in 2014, thousands of years after the Neolithic burial mounds had fallen out of regular use. Now Angel builds them, for customers who have chosen—when the time comes—to be laid to a prehistoric kind of rest. Barrows—which, when Googled, leads first to a page about an old fantasy video game—are, in this context, burial mounds that were commonplace throughout the British Isles during the early Neolithic period, between 4000 and 3000 B.C. From the outside, they typically look just like small grassy hills,…