During the Ripture War. The beasties were so many and so powerful, that in order to win the battle, the fighters sometimes just had to fall in order to protect the healers.

This is from the Tear battle near south gate. I don´t remember if we actually won or lost this one, but the fallen-formation is from the book.

Roowan and Urgelt are preparing to fall to fill up the remaining holes, that will prevent the greater wraiths from getting close to the healers. We others have formed a nice brick line.
And here is the final fallen-wall. If you can´t beat them, brick them..

The healers could then concentrate on healing the tear, which was the way to fight them. If we failed, we fell into the void, and that snell was lost. If we succeeded, the tear disappeared.
For more tales from the Ripture war see the RQ Library. Some visionstones can also be found in the RQ Vault.