The Shapes of the Medieval Ostensorium (Monstrance)

One of the features of the Ambrosian rite that many Catholics of the other Latin rites take note of is the shape of the ostensorium -- or monstrance -- used in that rite for processions, benediction and adoration of the Blessed Sacrament. In point of fact this vessel was (historically speaking) not solely used for the exhibitions of the Blessed Sacrament; they were used to 'exhibit' all manner of sacred objects -- relics for example.  To understand this is to understand the point we are about to discuss, which is that the shape of ostensorium we now tend to associate with the Ambrosian rite was in point of fact simply one of the earlier, at one time common forms of this vessel; it is not a unique Ambrosian form therefore -- though the Ambrosians are indeed unique in their exclusive retention and preservation of this particular form of ostensorium.

Benediction of the Blessed Sacrament in the Ambrosian Rite

In modern English usage we now use "ostensorium" or "monstrance" to specifically and exclusively refer to a vessel which is made to contain the Sacrament, while we refer to a "reliquary" to speak of vessels made to contain some sort of relic. However, given the fact this vessel had a wider use originally, possibly displaying the one or the other, one can perhaps better understand the form of this earlier shape of monstrance for clearly its design was intended to facilitate as broad a view as possible for its sacred contents -- whether that be the Sacrament or some relic. 

It is thought that the ciborium itself -- the chalice like vessel in which the Sacrament is reserved -- was at first what was used in such Eucharistic processions, but as Eucharistic piety grew in the middle ages, a specific vessel made for this purpose came to be crafted -- one which retained a ciborium like shape. Woodcuts from illustrations taken from a Missale Romanum dated to the second half of the 16th century also show this shape of ostensorium in use and one will see here its proximity to the contemporary from of ostensorium still used in the Ambrosian rite:

As Eucharistic piety continued to develop and be fostered, the shape of this monstrance continued to evolve, ultimately landing at the sunburst like shape that we are now so accustomed to -- the design itself lending itself not only as a visual suggestion of a burst of heavenly light shining forth much like a halo, but the rays also leading one's eye to the circular host contained therein. The first evidences of this shape can be found in the15th century. 

Of course it must be noted that, historically speaking, the forms and designs of the monstrance have been many-fold, not simply these two variations. Perhaps one of the best known popular variations still seen today in monstrance design is that which takes on a gothic form:

Many such historical examples can be found, however the oldest extant monstrance that we know of to date is one which is kept in the church of St. Quentin in Hasselt, Belgium, dated to the year 1286. It shows an ostensorium which has a tower like form, here shaped in the form of a hexagon and surmounted by a rood scene.

In this shape we can see echoes of both the circular, tubular shaped monstrance shown at the beginning of this article, as well as echoes of other shapes of monstrances that developed over the centuries.