who are sibllya & Diana ? why does portia mentioned them?

Sibylla and Diana, a prophetess in ancient time. Sibylla was famous for her extreme old age, and Duiana was a Roman goddess of feminine virtue and purity. Portia is saying that she will remain unmarried for the rest of her life,like Sibylla, or until a man chooses the right casket and makes her a virtuous girl like Diana.

Sibylla was a prophetess in roman mythology. Apollo granted her as many years of life a there were sand grains she held in her hand.

Diana was the goddess of viginity in Roman mythology. She was alsi the goddess of hunting and the moon.

They are referred here to explain Portia's resolve to remain a virgin like Diana even if she lives to be as old as Sibylla unless she is won in marriage by some suitor in the lottery of caskets.