GreatKhan12
Chieftain
In your mind what is the most critical and important technology in civ 4
I would argue that the most important tech in civ4 is Military Science.
It lets you bypass rifling for a long time--giving you grenadiers and safely leads you to machine guns and destroyers later. It gives you a huge naval advantage with Ship of the Line which are amazing naval units, and military academies are important.
By following this path of the tech tree, you will usually try to nail steel before hand.
I would rather have muskets/grenadiers/cannons than riflemen.
Having cannons while your opponent still has catapults and trebuchets is huge.
One of the terraforming techs for sure. Id pick Agriculture. No farms no cities. No cities no nothing. Roads can be emulated by water, mines in many ways too, cottages are not needed until midlate game. But lack of food is suicidal.
Agriculture is one of the few techs that you don't need to research for any other technology... so now this post feels like a challenge.
Will you be running a specialist economy? Oh wait I'm not meant to mention that.