English translation:
Dreaded day, that day of ire,
when the world shall melt in fire
told by Sybil and David's lyre.
Fright men's hearts shall rudely shift,
as the judge through gleaming rift
comes each soul to closely sift.
Then, the trupet's shrill refrain,
piercing tombs by hill and plain,
souls to judgement shall arraign.
Death and nature stand aghast,
as the bodies rising fast,
hie to hear the sentence passed.
Then, before him shall be placed,
that whereon the verdict's based,
book wherein each deed is traced.
When the Judge his seat shall gain,
all that's hidden shall be plain,
nothing shall unjudged remain.
The poem itself is a meditation and a paraphrase of the Revelations from the New Testament (see for example Rv 8,6
or 11,15) and deals with an apocalyptic subject matter. The structure is consistent: using paired versicles with equal number of syllables per line. Each versicle consist of 3 lines forming a tercet and the lines inside the tercets rhyme with each other.
Quantus tremor est futurus
quando judex est ventúrus,
cuncta stricte discussurus.
quando judex est ventúrus,
cuncta stricte discussurus.
This form is typical among late sequence verse structure and composing rhymed tercets of eight syllable lines were very much the norm by the mid. of 12th-century, not only for sequences but for new Office formularities as well). Seeing such progression towards regularities in composing a century before Alexander shows that there were indeed attempts to set up rules in compositions in order to make newly composed pieces (even if they were meant for liturgical use or not) easier to remember.
The beginning of the melody is a parody on the responsory verse of Libera me, Domine, de morte aeterna, and the whole sequence is in Mode 2. Phrase A uses almost the whole (so to say) 'official' range of the modus, begins on its dominant (reciting note) f and ends on the finalis d. Phrase B exceeds the ambitus of Phrase A but also ends on the finalis, while the melody of Phrase C leads back to the music material of Phrase A and also goes a fourth below the finalis.
Also in this case, the textual and musical material of Phrase C is not shortened, but its melodic progressions seem to lead back to the characteristics of Phrase A.
Used sources:
Taruskin, Richard: Music from the earliest notations to the Sixteenth century, Oxford University Press, USA (July 27, 2009), Chapter 3: Retheorizing Music, pp 88-89
Hoppin, Richard: Medieval music, (Norton, 1978), Chapter III, pp 64-66