“Afghanistan: Hidden Treasures From the National Museum, Kabul” begins its 17-month US tour on May 25 at the National Gallery. It’s full of surprises, starting with the survival of gold objects from the second century ad. A Soviet archaeologist, just before the nation’s 1979 invasion of Afghanistan, found 20,000 crowns, hair ornaments, earrings, and tiny models of animals—known as the Bactrian Hoard—in burial mounds. No one is sure where the cache was stored during that war, but in 2003 Afghan leaders opened a vault under central Kabul expecting to find bullion. What they found was the Bactrian Hoard, many pieces of which are in this 230-object show.The rest of the exhibit—silver bowls dating from 2200 bc; bronze, ivory, and stone sculptures depicting Greek gods from the second century bc; and first-century-ad vases and painted glassware imported from Rome, India, China, and East Asia—were found at three other archaeological sites. Closes September 7. After the US tour, the treasures will be returned to a building in Kabul designed to house the collection.