One of the most idiosyncratic of the many masses written on the "L'homme armé" cantus firmus, this setting was written clearly as a response to Josquin's L'homme armé mass Super voces musicales.¹ Its particular cantus firmus scheme offers an ostentatious canonic extension to Josquin's comparatively simple plan, in which the L'homme armé melody is presented on ever higher steps of the natural hexachord as the mass progresses (C, D, E, F, G, A). In Forestier's composition, the structural cantus firmus likewise appears on rising pitches of the hexachord which change between movements or sections, but a huge leap in complexity comes with the simultaneous (canonic) presentation of the same tune at its traditional 'default' pitch level of G within each section (see Table 1). The basic five-part texture (two cantus firmus-bearing Tenors and three free voices) is expanded starting in the Osanna to six voices with a third canonic voice; and the four-voice stacked canon of the Benedictus is transformed into a culminating seven-voice version in the final Agnus dei.

Table 1: Canonic cantus firmus pitch scheme

Section	Number of voices	Pitches (in order of entrance)
Kyrie I	5	G, C
Criste	5	G, C
Kyrie II	5	G, C
Et in terra	5	G, D
Qui tollis	5	E, G
Patrem	5	G, F
Et incarnatus	4	G
Et resurrexit	5	G, G
Sanctus	5	G, a
Pleni sunt	4	G, a
Osanna	6	G, A, d
Benedictus	5	A, D, G, c
Agnus I	6	G, C, D
Agnus II	5	E, d, G
Agnus III	7	GG, C, F, G, c, f, g

Among the various structural peculiarities of Forestier's mass is its penchant for (near-)exact repetition of polyphonic material, in connection with the repetitions within the cantus firmus (L'homme armé has an overall ABA structure and contains numerous smaller repetitions of melodic-rhythmic segments). In a few cases this appears as a brief echo on a local scale - e.g., Credo, mm. 169-79, where Superius and Bassus match their repetitions to the canonic restatement of a single cantus firmus phrase, producing a direct formulation of melodic motives which they had already been developing from m. 159 onward. At a greater temporal distance, other repetitions take a cue from the tripartite form of the cantus firmus to lend a circular form to certain sections: Credo, mm. 6-17, matches mm. 35-46, and the Osanna opens and with the same six-voice material (Sanctus, mm. 43-6, matches mm. 72-5). The more typical practice, both in L'homme armé masses and elsewhere, is to provide repeated cantus firmus segments with new polyphonic elaborations each time, even if these recall the earlier statements in some way; Forestier's procedure in this case has an antecedent mainly in the masses of Guillaume Faugues with their sectional repetitions (including his Missa L'homme armé, probably the first of the canon-based settings and surely known to Forestier). It cannot be said that this was a matter of contrapuntal expediency, when the compositional difficulty lay in the construction of the canon and decidedly not in the addition of freely-composed voices to this structural backbone. Clearly the repetitions represent a deliberate formalistic move of a sort not often encountered at the period.

The idea of circularity implied by the polyphonic repetitions is made explicit in the Tenors' notational form, which always indicates a return to the beginning of the section rather than modifying or restating the A section of the tune. Even more striking in this respect is the form of the final fully-canonic Agnus dei, which features the same return to the start of the section in each voice, but offers no indication of a stopping point: the section could repeat ad infinitum, and indeed any ending must be chosen arbitrarily (the present transcription ends where the last voice has stated its material once in its entirety). Again this is a culminating statement by Forestier, focusing the earlier hints at cyclicity into a single form and eliminating everything but the cantus firmus. There is almost certainly some extra-musical symbolic intention here, connected to the composer's concern to place the cantus firmus at every pitch level and in every hexachord within the Gamut. The Christological interpretation of L'homme armé usage within the mass offers paths for further speculation and a connection to the canonic inscriptions (e.g., "omnes post me venite" within the final Agnus dei).²

Transmission

Although suriving in four separate manuscript copies, the mass offers a more restricted image of transmission than this would suggest: all of these sources stem from the Habsburg-Burgundian court scriptorium during the tenure of Petrus Alamire. This situation testifies surely to the status of the piece - this is a large number of Alamire copies for a work by a composer with no apparent connection to the courts of Burgundy or France - and it produces an interesting view of the levels of variation which could arise within exemplars of the same music written by the same scribes.

Once again the canons take center stage, this time as a locus of concern for both scribes and performers. No two sources contain precisely the same set of verbal instructions (see Table 2 below); and the varied usage of French and Latin inscriptions, sometimes poetic, sometimes purely 'functional', positioned variously in relation to the affected voice parts, confuses any attempt to establish which canon texts are the products of Alamire and which could be linked more closely to the composer's conception of the mass and its possible symbolic connections. Not a single canonic inscription appears in all sources, but several call for greater attention. The text "Quatuor quaternionibus", describing the four-part canon at the fourth in the Benedictus, is the only instruction to appear in the copy of the Occo Codex, where it has been added by a later hand that corrected much of the manuscript (see the Occo Codex project Introduction); this inscription is also present in two of the remaining three sources. The four-line poem connected to the circle-canon of the final Agnus dei ("Septenarius ut sum...") appears in all non-Occo sources, and would seem to have the securest claim as an 'essential' element of the composition.

On the other hand, the explicit French and Latin texts in VatS 160, e.g., "Ung ton plus bas per FA" in the Patrem, did not end up in any other copies of the composition. Their very nature as an extended explanation of Forestier's plan makes them suspect as 'authorial' elements, serving instead to aid performers in resolving and understanding the canons immediately. This practical concern was answered equally in several resolutions included in different copies of the mass. VatS 160 follows the final Agnus dei with an extra opening resolving this section into seven separate voice parts (ff. 109v-110r). A small sheet inserted into the Qui tollis in JenaU 3 offers a resolution of the canon in that section, texting it with words of the Mass Ordinary; the verso bears the name of Adam Rener, composer and singer at the court of the Elector of Saxony, offering thus an exceptional glimpse of an extant performance aid.

Table 2: Canonic instructions in sources of Forestier's Missa L'homme armé

Section	Source	Instructions
Kyrie I	VatS 160	Canones super voces musicales et primo In subdyapente per VT
Kyrie II	VatS 160	vt supra
Et in terra	VatS 160	In sub dyatessaron per RE
Qui tollis	VatS 160	Precedam in sub semidytono per MI
Patrem	VatS 160	Vng ton plus bas per FA
Et resurrexit	MontsM 766	...pausando
	VatS 160	Canon in vnisono .
	VatS 160	In eodem tono per SOL
Sanctus	VatS 160	Vng ton plus hault per LA
Osanna	JenaU 3	Vng & deux sont trois Et le quart pour les galois
	MontsM 766	...troys et le quart pour...
	VatS 160	CANON. vng et deulx sont troys . et le quart pour les galoys .
		La primiere va deuant
Benedictus	BrusBR IV.922	Canon. Quatuor quaternionibus
	JenaU 3	Benedictus supra bassum
		Canon. Quatuor quaternionibus
	MontsM 766	Canon. Quatuor quaternionibus
	VatS 160	Benedictus supra bassum.
		Alter post alterum per dyatessaron intensum sequatur
Agnus I	VatS 160	In subdyapente subdyatessaronque
Agnus II	VatS 160	Agnus secundus supra contratenorem.
		Tres in carne vna.
		Tertia secundam Secundaque primam sequetur
Agnus III	JenaU 3	Canon Septenarius vt sum Omnes post me venite Sequens alter alterum Tempus vnum sumite
	MontsM 766	[very light; appears to be same as JenaU 3]
	VatS 160	Agnus tertius supra bassum.
		Septenarius vt sum Omnes post me venite. Sequens alter alterum. Tempus vnum sumite.

Pre-existent material: L'homme armé, monophonic chanson treated as canonic scaffolding cantus firmus usually in Tenors

Transcription from NapBN 40, f. 58v

Editorially supplied material: Plainchant intonations of Gloria and Credo supplied from Paris, Bibliothèque nationale, MS lat. 14452, f. 243r-v (Gradual of St. Victor of Paris, 13th century, with additions dated 1567)

Notes
[1] See David Burn, 'Further Observations on Stacked Canon and Renaissance Compositional Procedure: Gascogne's "Ista Est Speciosa" and Forestier's "Missa L’Homme Armé"', Journal of Music Theory, 45 (2001): 73-118. A more general description of Forestier's mass appears in Jacques Barbier, 'Un homme armé à Bruxelles: Étude de la messe de Mathurin Forestier contenue dans l'Occo Codex', Revue belge de Musicologie, 55 (2001): 53-68.
[2] On this interpretation of L'homme armé, see Craig Wright, The Maze and the Warrior: Symbols in Architecture, Theology, and Music (Cambridge, MA and London: Harvard University Press, 2001), esp. pp. 164-88.