The death of the Emperor Joseph II not only marked the end of an era in Austrian history, it ushered in a new golden age in secular music: the restrictions on such music imposed by Joseph were now abolished, and monasteries and aristocratic dynasties once again vied with each other in mounting increasingly elaborate religious services. With the leading composers of the day creating a wealth of sacred works that combined contemporary stylistic devices with traditional elements redolent of the splendours of the Baroque.
At the same time, secular pieces would often find their way into the sacred repertory: suitably reworded, famous arias were performed as motets, and lengthy instrumental works were incorporated into the liturgy, notably as Epistle or Offertory sonatas. This somewhat free-and-easy approach to sacred music gave rise to criticism, not least on the part of ultraconservative Catholics. Curiously enough, the greatest offence was caused by the six great masses that the universally acclaimed Joseph Haydn wrote following his triumphant return from London in 1795. Haydn was reproached for the fact that the dominant mood of these works was "not the solemn seriousness that befits the temple of the Lord, but profane, naïve wit and an inappropriate frivolousness". So seriously was this criticism taken that his masses came close to being banned from St Stephens Cathedral in Vienna.

Following his return from his second visit to England in 1795, Haydn resuined his duties with Prince Nikolaus II Esterhátzy, one such duty involving the composition of an annual mass to mark the name-day of the Princess Marin Hermenegild. The first of the composer's six masses intended for this occasion is believed to have been the Missa in tempore belli, which probably received its first public performance in the Bergkirche at Eisenstadt on 13 September 1796, although this has been disputed by the Haydn scholar, H. C. Robbins Landon, who suggests that a performance of an otherwise unnamed work that is known to have taken place in the Basilica Maria Treu of the Piarists (otherwise known as the Piaristenkirche) in Vienna on St Stephens Day (26 December) 1796 is more likely to have been the mass’s first official airing.
It emerges from the autograph full score that the forces that Haydn originally envisaged were strings, organ, oboes, bassoon, trumpets and timpani; clarinets were used only in a handful of movements, where they double the oboe parts. But the discovery of an additional set of parts with original entries in Haydn's own hand indicates that the composer later enlarged the instrumental forces: clarinets are now found in all six movements, a flute has been added to the "Qui tollis" and the trumpets are now doubled by horns.
The German diplomat, Georg August Griesinger, who was on friendly terms with Haydn, reports on the genesis of the Missa in tempore belli as follows: "In 1796, at a time when the French were encamped in Styria, Haydn wrote a mass to which he gave the title 'in tempore belli'. In this mass, the words 'Agnus Dei, qui tollis peccata mundi' are declaimed in a curious fashion, with timpani accompaniment, as though one could already hear the enemy approaching in the distance."
Haydn wrote at a time of national emergency a circumstance reflected in the score. Napoleon's troops were at the gates and it was regarded as a crime punishable by death even so much as to speak of peace as long as enemy forces were in the land. For Haydn, the words of the Ordinary of the Mass offered a unique opportunity not only to speak of peace but positively to demand it with every musical means at his disposal. This is particularly clear from the Kyrie, the theme of which, first stated by the soprano soloist, is taken up by the choir and repeated in increasingly urgent statements, while brief interjections from the four vocal soloists add to the sense of insistency. The humble entreaty, "Have mercy upon us", seems, on occasion, to be literally rebellious in tone.
The Gloria is symmetrically structured, with two thematically related outer sections, the superficial festiveness of which is repeatedly undermined by seemingly threatening instrumental gestures, framing an Adagio in A major contested by bass soloist and choir and invested with a particularly rapt atmosphere by the obbligato cello’s mellifluous line and the writing for the solo flute.
The Credo is launched with a fugue that gives way to an “Et incarnatus” of almost oppressive vividness in which the bass's introduction is taken up and developed by the other soloists and choir. It leads directly into the “Crucifixus” and, thence, to the ascending scales that herald the festively joyful "Et resurrexit". A double fugue with solo interpolations brings this section of the Ordinary to an end.
A brief two-part Sanctus is followed by a more broadly structured and lyrical Benedictus, which, largely reserved for the vocal soloists, is notable for the way in which the music modulates from C minor to the major at the word “Hosanna”.
It is in the Agnus Dei, finally, that we find the famous timpani solo that has generated so much controversy but to which the Missa in tempore belli owes its name in the German-speaking world - the "Paukenmesse". A simple melody, entrusted to choir and strings, is followed by the muted yet implacable rhythm of the timpani, which is accompanied by oppressive syncopations on the first violins and sustained notes on the oboes. According to Haydn’s early biographer, Giuseppe Carpani, the timpani was to be struck in the French manner here. The threat presented by the imminent approach of war is thus expressed in particularly striking fashion, climaxing in the shrill wind fanfare that culminates in the general outcry on the words “Dona nobis pacem”.
Haydn was also conscious, of course, of the psychological effect of the timpani rhythm, which was intended to encourage those for whom the drum is beaten and to inspire fear and terror in those against whom it is aimed. Haydn had already tried out this twin effect in his “Military” Symphony Hob. I/100, a piece which, by its very nature, is likewise an anti-war work. Now it is the timpani that are used, as it were, to confront God with the whole appalling horror of war and, by virtue of its increasingly urgent entreaties, to force from Him the peace so desperately longed for.

The last of the four Marian antiphons, the Salve regina is sung at the end of Compline - evening prayers - between Trinity Sunday and Advent. 17th-century settings often involved lavish instrumental forces and were used as motets at Marian feasts.
It is not known for what occasion Haydn wrote the present Salve regina in G minor Hob, XXIIIb:2. It is scored for four vocal soloists, concertante organ and strings and, according to a note in the autograph score, was written in 1771. An organ solo contained in the same autograph points in the direction of the Chapel of the Brothers of Mercy in Eisenstadt, for which Haydn also wrote his Little Organ Solo Mass.
The piece is cast in the form of a large-scale sonata da chiesa (Adagio-Allegro-Largo/Allegretto) and acquires charm as a result of its rhetorical intensity and the multifaceted variety of the emotions that it portrays.