MILAN, ITALY—A temple thought to have been dedicated to the goddess Minerva has been discovered beneath Milan’s cathedral, and a stone floor and a section of an arcade of the ancient Mediolanum Forum have been found under the basement of the seventeenth-century building that houses the historic art gallery, Pinacoteca Ambrosiana, and the library, Biblioteca Ambrosiana. In A.D. 292 Mediolanum became the capital of the Western Roman Empire, and it remained so until 402.