Historical clue formulations

• Answer provided by the magic object named twice in the circled squares — 2015-06-06
• C. P. and E. B.'s essay on purity? — 2009-10-11
• Symbol of purity — 2008-02-11
• Woman associated with seven other answers in this puzzle — 2005-01-04
• Friend of 21-Across — 1994-09-09