Two weeks after calends, approximately

The answer to this crossword question is “MARCH.” In ancient Rome, the calendar was divided into months that began on the calends (1st day) of the month. The ides were approximately in the middle of the month, falling on the 15th day of March, May, July, and October, and on the 13th day of the other months. Therefore, the phrase “Two weeks after calends, approximately is IDES” refers to the fact that the ides of March (approximately two weeks after the calends of March) were a significant date in the Roman calendar and remain famous for the assassination of Julius Caesar.