Yeah but the actual answer in 3e is the wizard flies 40 feet in the air, invisible, and blasts the lot into craters, before heading home for a nice spot of tea. 24 level 1s might challenge a level 10 fighter, if only because fighters are terrible, but I tend to doubt it.I voted more than 16.
In 3.x, it would take approximately 24 EL 1's to equal an EL 10. (That's a basic calculation, 3.x EL math can get a bit more complicated when you add additional factors).
Ignoring EL, just looking at HP ... the level 10 fighter in 3.x has probably 10x the hp of the level 1 fighter and greater AC/saves. So durability is >10x.
The greater accuracy, damage, and attacks per round of the 10th level fighter probably also indicates a >10x damage per round performance.
So it looks like durability and damager per round are both greater than 10x for a level 10 fighter versus a level 1.
Heh, I remember a thread some time back where we did a thought experiment pitting 1 million level 5 PC's vs a 20th level wizard lich. You could make a reasonable argument for the lich winning the confrontation.
The million level fives all get into groups of 125 and draw lots. Those who win in each group of 125 kill all the remaining level 5s, earning enough experience to level up to level 13 (at which point they stop earning experience from killing level 5s). The level 13s all get into groups of 125 and repeat the process. This handily brings them all up to level 20. There were 64 groups in the second stage. I think, if my experience calculations work.
I suspect 64 20th level characters, even with whatever gear they can cobble together from all the 5th level PC gear they have, will probably own a 20th level Wizard Lich. You can probably optimise the process further to increase the proportion of the starting million that survive. I believe if you stop at 16th level, 320 survive, and I wouldn't bet on one 20th level Wizard Lich against 320 16th level characters.
EDIT: It's also possible to optimise further, as you can choose not to level up even if you have earned enough experience to do so, but I can't be bothered to do the maths to work out the best way to do that.

Any trick the Lich can pull off, the 64 survivors can too. And they'll be able to do it better, because they'll have a variety of Wizard prestige classes (if there aren't 64 Wizards among the initial million, I'd be very surprised). Letting anyone but full casters be in the surviving 64 would be a terrible plan.

(Dungeons & Dragons)
Rulebook featuring "high magic" options, including a host of new spells.