This lorica (breastplate) prayer is called “Alexander’s Breastplate” because it is between two poems about Alexander the Great in the Welsh Book of Taliesin.
On the face of the earth
his equal was not born,
Three persons of God,
one gentle Son
in the glorious Trinity.
Son of the Godhead,
Son of the Manhood,
one wonderful Son.
Son of God, a fortress,
Son of the blessed Mary,
Son, Servant, Lord.
Great his destiny,
great God supreme,
in heavenly glory.
Of the race of Adam
and Abraham,
and of the line of David,
the eloquent psalmist,
was he born.
By a word he healed
the blind and deaf
from every ailment;
the gluttonous, vain
iniquitous, vile, perverse,
to rise toward the Trinity
by their redemption.
The Cross of Christ
is our shining breastplate
against every ailment.
Against every hardship
may it certainly be
our city of refuge.
Source: Book of Taliesin, Welsh, 10th-14th Century, excerpt
The Four Ancient Books of Wales, 1868, p. 557-558.
Source of this version: Prayers from the Ancient Celtic Church.
Original in Old Welsh:
Ar clawr eluyd y gystedlyd ny ryanet.
Teir person duw. vn mab adwyn terwyn trinet.
Mab yr dwydit. mab yr dyndit. vn mab ryued.
Mab duw dinas. mab gwen meirgwas. mat gwas gwelet.
O hil ade ac abrahae yn ryanet.
O hil dofyd dogyn dwfynwedyd llu ryanet.
Dyduc o eir deill abydeir o pop aelet.
Pobyl ginhiawc. goec gamwedawc salw amnyned.
Rydrychafom erbyn trindawt gwedy gwaret.
Croes cristyn glaer. lluryc llachar rac pop aelat.
Rac pop anuaws poet yn dilis dinas diffret.
http://www.ancienttexts.org/library/celtic/ctexts/t27w.html and http://www.maryjones.us/ctexts/t27w.html
A Collection of Prayers 