Something of a mongrel, this window would originally have comprised two main sections - the lower half dedicated to the life of St Apollinaris (or Apollinaire), the first Bishop of Ravenna, the upper half containing a (possibly) unique stained glass depiction of the Celestial Hierarchy of Pseudo-Dionysius. Then, in 1328, one Canon Guillaume Theirry paid for an altar to be installed in this bay, or on one of the adjacent columns. He had the lowest register of this window replaced with a set of panels, painted in the latest style, depicting the altar's titular saints in delicate grisaille, and commemorating forever his act of generosity in a lengthy inscription. It is impossible to know for certain what the now missing panels may once have contained but we may be allowed an educated guess or two. The available space would perfectly match a wide border along the bottom, like the one surrounding the rest of the window, plus a register of exactly the same pattern as the row containing panels 13, 14, 15. The space now occupied by panel 05 would probably have contained the only notable event in the Vita of St Apollinaris prior to his arrival in Ravenna - namely St Peter in Rome giving him his mission (always a crucial scene for saints who were claimed to be part of the direct Apostolic succession). That would leave the two bottom quadrants for signature panels.

The upper half of the window contains a representation of the Celestial Hierarchy, based on the eponymous book by the 6th century Syrian Christian mystic known as Pseudo Dionysius the Areopagite. This taxonomic schema is a most unusual topic for a lancet window - certainly I know of no other examples from the period. The text outlines nine different choirs of divine beings, from Angels to Seraphim, in ascending order of their closeness to God. As part of his mystical theology of light, Pseudo Dionysius describes how each level can only perceive directly the level immediately above itself and is incapable of direct experience of the divine light, as are we. Nevertheless, he argues, we can transcend these limitations to some extent by the spiritual exercise known as anagogy, in which the subject's perception can rise beyond the earthly through contemplation of the manifestation of the divine in earthly things (theophany). The work was translated into Latin by Eriugena in the 9th century and was relatively well known in the 12th century. Abbot Suger of St Denis, Hugh of St Victoire and and Theirry of Chartres (no relation to the donor of this window's later additions) all wrote about its influence. Nevertheless it remains a relatively rare piece of iconography outside manuscript illumination, with just this one window and two examples in portal sculpture - one of them situated very close to this window in the south portal at Chartres.

Quite why this window should have been divided into two halves at all is also unclear. The medallion pattern is consistent throughout, so it was presumably always planned this way. The designers at Chartres were perfectly adept at stretching out the visual vitae of far more obscure saints than Apollinaris to occupy as many panels as required - and they were scarecely short of openings into which to fit their stories. Nor am I aware of any reason for linking St Apollinaris with the Celestial Hierarchy (St Denis would have made a far more obvious choice, given his standard conflation with Pseudo Dionysius), though it is possible that some quirk of the Chartrain liturgy or some other local circumstance gave rise to an association now lost.