I believe the answer is: Euclid and Pythagoras.
Euclid alexandria was a famous mathematicians who is regarded as the father of Geometry and phytagoras was known for developing the phytagoras formula to measures sides of triangles. Their accomplishments were really crucial because it is still used to calculate correct measurement in modern day architecture and engineering.
The Twin Towers.
Also, to scare people, for them to know that Al-Qada exists.
According to Walter Cronkite the tet offensive was a stalemate and neither sides win the battle but it changes his view after he went to Vietnam and sees what is happening to the US soldiers fighting a war that both sides neither wins. Even though he is silent strong supporter of US involvement in the war but after seeing firsthand it changes his point of view of US involvement in war and rather than victors it is better to negotiate as the people who pledge to protect democracy in the war.
