Step 1: Recall the year directly:
1235 A.D. marks: Death of Sultan Iltutmish.
Step 2: Provide brief context:
Sultan Shams-ud-din Iltutmish, who consolidated the Delhi Sultanate and completed the Qutub Minar, died in 1235 A.D.
Final Answer:
\[ \boxed{\text{Death of Sultan Iltutmish}} \]