I was able to see lanius from the entrance to to that area, granted just the top of his head is all. I think you have to walk up the hill for him to spawn though. Just dont talk to him once he pops up and retreat all the way back the entrance. From there i could see lanius and 2 soldiers flanking the entrance to the tent. I was able to snipe all 6 f the soldiers by the time lanius got to where i was at.

my advice is take your AM rifle, crouch and sneak up the ramp to lanius tent. when you get to the first u-turn, hop on the rocks to your right. wait until it says you're hidden, line up your shot and pop the legate in the cranium. if it doesn't kill him, he'll be badly wounded.

How to do it at low level without much effort:
Step 1: kill goons
Step 2: shoot him/set up mines etc before talking to him
Step 3 for ranged characters: Find a nice wide obstacle, jump over it and fill him with bullets. Flame based weaponry is a bonus since I noticed he has a knack for regenerating health. Everytime he gets close just jump over/on another rock.
Step 3 for melee characters: svck on buffout, med-X, turbo, psycho, and a whole bunch of food. Charge at him with golden gloves and strafe fight him. When he gets knocked out switch back to one of the many ballistic fists you should have found on a previous centurion and kick him while he's down.

The real hard part is if you sided with house/yes man since those securitrons are very slow at shooting the ncr rangers before they turn you into swiss cheese.

I really, really don't understand what's giving you folks so much trouble.

I beat Lanius at level 16, on hardcoe, limbs crippled to all hell cause I ran out of doc's bags and hydra, and all my companions were dead and I had to walk uphill BOTH WAYS to get there (okay the last one's not true but everything else is).

Here's the gear:
Sniper rifle (not even modded) using AP ammo (makes a HUGE difference).
Hotkey'd stimpacks (remember I was on hardcoe so I couldn't just spam the hell out of them, but they still helped).
Salvaged power armor (I never got training on this character and just picked some of the armor up from some NCR folks I blasted).
1 Stealthboy.
Drugs

Here's the plan:
Clear the other goons before initiating contact with Lanius.
Position yourself behind the Legate, in the grass at the bottom of the winding path that leads up to him (don't get too close as to engage him in conversation).
The key here is that you want to get one perfect shot off before initiating dialogue with Lanius.
If you have a high enough sneak let the round fly and put one in the back of Lanius' head (this probably won't kill him).
If not, pop a stealthboy and initiate a sneak-attack on him (again, shooting for his head).
The goal is NOT to kill him right off the bat, if you do this it seems to end up bugged and you're stuck, you need to let him get a word with you (but by this point you should have shot him once bringing his overall health down to ~1/4).
Say whatever (this isn't a guide for talking your way out as that should be more self-explanatory).
As soon as combat reinitiates, pop as many drugs as you can (Psycho, Jet, maybe Turbo).
Enter VATs, put as many rounds as you can into the Legate's head (you should be close enough to not miss).
Win.

Seriously, he should be dead as a door-nail if you do all this. His goons stop spawning when he dies (I think you still need to kill them, but they don't hit anywhere near as hard as he does (did, hah!)).

If you can follow directions, you can kill Lanius. Unless you chose Energy weapons, cause they svck and you're probably screwed, I hope you have a high speech skill to go with it.

I hear ya! I went at him (no followers) at least 15 times (level 27) and got hammered - I tried chems, weapons, etc. I finally decided to go back and level to 30 to get my speech to 100. The only way I personally have a chance of getting by him. I'll be coming through with the NCR next time. Maybe that will help.

Get inside the camp, kill evertone before you reach thorugh the 3nd gate . Get Veronica with T-51b power armor and those fists you get from the camp.. place 5 pule mines and c4 explosives near the stairs... Get a far.. Use the guass rifle to kill one of the two Guards(100 energy weapons). then RUn like hell to the corner.... By that time he would have lost half his 1/3rd of his health at the mines, Use Guass rifle to cripple his legs. then its killed him and his gang with energy weapons(I have the perk which enemies explode when you kill them with energy weapons). Stay close to Veronica and keep healing her. She is a real Kick ass

Seriously Folks. (Normal Diff- Cass with an AM Rifle in tow)
I am getting *Puh-hounded* at Caesars HQ after the Hoover Dam. Okay- in my Defence I am Level 20 but am toting some relatively serious stuff.
I have 1 mine, which I judiciously lay at the staircase before Lanius (I know he deserves many more-) Then I pump all the chems and books I have with no shame at all. (My body is an Amusemant Park, not a Temple...)
Forget talking to Lanius, I'm lining him up with the Matter Modulator/Hunting Shotgun/Incinerator - and he turnes to me with that look of implacable distaste that only his mask can give and rushes me. Six dudes pop out of the Tent to join the fun and I am smashed to pieces across the rocks of the lower Camp.
Q1: Am I too young to be messing with Lanius? (Level 20...)
Q2: Should I be packing a *lot* more mines?
Q3: The RCW RIfle. Should I endeavour with it?
So I throw the Problem Open - Whoever reads this is Awesome.
Who's Awesome? You're Awesome.

Melee, huh? My experience with F3 leaves me all...delicately predisposed about it all. Yet I look at the Forums and read Tales of beefed up Dude(ttes) pounding all and blasted sundry. Give me some time to screw up my Courage (I've screwed everything else!