The first major museum exhibition ever devoted to the art of Armenia — officially its “medieval” era, but in fact spanning nearly 1,500 years — bulges with weighty stone crosses, intricate altar frontals and flamboyantly illuminated Bibles and Gospel books unlike any manuscripts you’ve seen from that time. Armenia, in the Caucasus Mountains, was the first country to convert to Christianity, in the fourth century, and the richly painted religious texts here, lettered in the unique Armenian alphabet, are a testament to the centrality of the church in a nation that would soon be plunged into the world of Islam. By the end of the Middle Ages, Armenian artists were working as far afield as Rome, where an Armenian bishop painted this show’s most astounding manuscript: a tale of Alexander the Great that features the Macedonian king’s ship swallowed by an enormous brown crab, hooking the sails with its pincers as its mouth gapes.