CREATE TABLE table_54748 ("Father" CLOB, "Birth" CLOB, "Marriage" CLOB, "Became Queen" CLOB, "Ceased to be Queen" CLOB, "Death" CLOB, "Spouse" CLOB)

When did the person who died on 6 Dec 1240 get married?
SELECT "Marriage" FROM table_54748 WHERE "Death" = '6 dec 1240'
SELECT "Marriage" FROM "table_54748" WHERE "Death" = '6 dec 1240'