From the Revolution to 9-11, New York has honored its heroes with civic and community memorials, and tributes to its fighting regiments. This treasure house of memory asks us to reflect on those who gave their lives and those who remember them, and to consider how even the highest sacrifices may be forgotten. This pre-Memorial Day conversation with Cal Snyder, Marine Corps veteran and author, and Ken Jackson, Columbia University History professor, is the culmination of three walks led by Mr. Snyder to renowned memorial sites of New York. $12 (members, students, educators, seniors $6) The New-York Historical Society, 170 Central Park West at 77th St. To reserve tickets, call (212) 485-9205. Charge your order to Visa, Mastercard or American Express. Advance payment is required to guarantee a spot.