Some years past I acquired by osmosis or other means a few lines of
poetry as follows:
“That girls are raped and two boys beat a third,
Were axioms to him who had never heard,
Of a world where promises are kept,
And one may weep, because another wept.”

I’m sure that my memory has distorted these lines, but I would like to
determine the source.  I thought it was Auden but have been unable to
confirm this.

Hello,

You are correct, it IS W. H. Auden, and you pretty much have the
passage as it's written. Here follows the short passage and a link to
the full poem below.

"A ragged urchin, aimless and alone,
   Loitered about that vacancy; a bird
Flew up to safety from his well-aimed stone:
   That girls are raped, that two boys knife a third,
   Were axioms to him, who'd never heard
Of any world where promises were kept,
Or one could weep because another wept."


Search Strategy:

"girls are raped "two boys" "beat a third" on google:
://www.google.com/search?q=+%22girls+are+raped+%22two+boys%22+%22beat+a+third%22

"The Shield of Achilles" on google:
://www.google.com/search?q=%22The+Shield+of+Achilles%22


Additional Links:

Full text of "The Shield of Achilles":
http://www.poets.org/poems/poems.cfm?prmID=1393


Thank you for the opportunity to answer your question, if you require
more information, please clarify the question, or if you find this
answer satisfactory, please feel free to rate it. Thank you!
  
skermit-ga

These three sites may be of interest in analyzing the meaning of the
poem:

Louisiana Tech University
http://www2.latech.edu/~bmagee/201/auden/shield2_w_notes.htm

Sparknotes: Modernist Poetry
http://mb.sparknotes.com/mb.epl?b=121&m=419786&t=154526

Echomyst's Elysium
http://www.geocities.com/echomyst/literature/auden.html

"The Shield of Achilles" is available in Auden's "Collected Poems,"
edited by Edward Mendelson. This excellent collection contains all the
poems that Auden wished to preserve, in versions approved by Auden
before his death.

Amazon.com
http://www.amazon.com/exec/obidos/ASIN/0679731970/qid=1035338273/sr=2-1/ref=sr_2_1/002-6938295-6108863