Diablo 3 Walkthrough Part 23: Last Stand of the Ancients

You arrive at the Festering Woods. Your objectives are:

The Broken Blade
Retrieve the Beacon of Honor from Warrior's Rest (0/1)
Retrieve the Beacon of Light from the Crypt of the Ancients (0/1)

Keep going northeast in the Festering Woods, following the trail. The road will soon branch. Turn right at the fork. You will be fighting your way through ghouls, enraged phantoms, and other types of ghosts. Turn left at the next junction, then head towards the yellow circle in the center. Climb the stairs and interact with the memorial stone near the dead soldiers. This unlocks an event:

Last Stand of the Ancients
Defeat the invaders

Undead Ghouls, Returned, and Enraged Phantoms will start climbing towards the top. If you have ranged attacks, now is a good time to use them as the enemies approach. If you have the Scoundrel on your team, as this strategy guide suggested, he will shoot arrows at the monsters as they climb the hill. Another wave of attacks will commence, including Ancient Heroes (Nightmarish Minions) and finally an elite boss, such as Uzay the Blasphemous (Nightmarish).

Note that the waves of enemies can be massive, so even if you can thin them out with ranged attacks, eventually some might make it to the top of the hill. Try not to get surrounded, you can run down yourself and fight from the more open road if you feel cornered. Use health globes as their appear, and be ready to click on health potions in your action bar. If you die, at this level you will have a death penalty (in addition to being revived at checkpoint), and you will see a message such as:

You have died
Your items have lost 10% durability
Revive at last checkpoint

This death penalty starts at level 10, and your armor and items will take damage with each death. It can be expensive to repair your items if you die a lot, so tread carefully and follow the tips in our strategy guide for the best gameplay experience.

Once you clear these waves of enemies, you will receive the following achievement:

Last Stand of the Ancients
Complete the Last Stand of the Ancients event

It is now time to proceed with the main quest, The Broken Blade