Two years ago, archaeologists excavating an ancient grave at Pylos in southwestern Greece pulled out a grime-encrusted object, less than an inch and half long, that looked like some kind of large bead. They put it aside to focus on more prominent items, like gold rings, that also were packed into the rich grave.

But later, as a conservator removed the lime accretions on the bead’s face, it turned out to be something quite different: a seal stone, a gemstone engraved with a design that can be stamped on clay or wax.

The seal stone’s image, a striking depiction of one warrior in battle with two others, is carved in remarkably fine detail, with some features that are barely visible to the naked eye. The image is easier to appreciate in a large-scale drawing of the original.

“The detail is astonishing, especially given the size. Aesthetically, it’s a masterpiece of miniature art,” said John Bennet, director of the British School at Athens, an archaeological institute.