Introduction

THE plan form of the Greek theatre supplied a motive which was adapted to a variety of purposes during Roman and subsequent periods: this is known as the “D” or Tribune plan, and it has long been accepted as a suitable form for “exedrae” and places of assembly. The earliest examples, such as those supposed to have formed subordinate features of the vast Roman thermae, were covered with semi-domes and were open to the outer air: it was in these places that poets and philosophers declaimed. There are few instances of this type of building to be found intact amongst the ruins of antiquity, but from the conjectural restorations made by various authorities, notably Canina, Durand and Blouet, some examples have been selected for illustration.

The transition from the simple exedra of small size to that of more involved interest is by easy stages, for the principle remains constant and will be readily understood from the examples illustrated. It is possible to vary the system in many ways according to the disposition of columns, colonnades and subsidiary features, while to the plan on a large scale may be added a series of semi-circular niches opening out of the enclosing wall.

The “D” plan as an architectural motive on a large scale first made its appearance at the close of the eighteenth century in the Chambre des Pairs of the Luxembourg, Paris. This was followed by the splendid interior of the Chambre des Deputes, which in turn served as a model for the Sorbonne, the most celebrated instance of its use. Further examples of its application can be instanced in the design of the State Capitol, Washington, at the beginning of the last century, and in almost every Parliament House of note on the Continent. In England, however, this ideal form has not received the attention it deserves.

The “D” plan in principle is one intended to give ample space in the auditorium, a central position for the speaker, and scenic display in the architectural treatment. The nearest approach in England to this type of plan is to be seen in the interior design of theatres, particularly those built from about 1770 to 1860, but in nearly every case the theatres built during this period approximate to a horse-shoe rather than to a “D” plan.

It is important that the student should become acquainted with this form of plan as an independent type before attempting to incorporate it in a complicated system of planning in which it is combined with various other features. Generally, such a form becomes the focal point in the arrangement of a building, and its approaches and connections need most careful adjustment. There are occasions when this particular plan can be treated as an isolated building with the addition of a portico, and at other times the basic D shape alone can be used as a connecting link, such as a courtyard between groups of buildings. There is no limit to the variety of treatment to which it lends itself, and experience has proved that from many standpoints the D plan is satisfactory.