The concept of history in the Middle Ages was not what it is today, as visitors to the J. Paul Getty Museum’s new exhibition of manuscripts will see. In an eye-popping image from “Romance of Alexander,” a book made in the 1290s, an unknown artist illustrated a yarn about Alexander the Great making an underwater expedition. Enthroned in a glass diving bell, below a whale that gobbles up much of the pictorial space, the regal explorer calmly observes a colony of nude people, earthly beasts and fruit trees living at the bottom of the sea.,0,6746819.story