Schwetzingen - Schlösser-Magazin

III.
Fig. 1: Wilhelm Schweitzer,
survey before 1933, ground
floor plan (From: Martin 1933,
p. 314, Fig. 301).
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III. Architectural Features
Architectural Design
The Temple of Mercury was built of solid
masonry as an artificial ruin over a hexagonal
ground plan with four accessible vaulted
storeys. Sandstone and tuff are used for
the facing, but also for structural purposes,
although in parts unseen brickwork provides
the structural core. The materials have been
layered into a composite system. The lowest
storey is concealed within a landscaped hill
and can only be seen and entered from the
south. Three doorways lead into the ground
floor, and every side containing an entrance
looks the same, with no principal façade.
Findings on site confirm what Leger describes
in his guide to the gardens of 1828. The
exterior of the tuff ruins were originally of
a dark reddish brown. The relief in weatherresistant
stucco is reminiscent of marble
carving. The space on the ground floor took
its atmosphere from a yellowy droplet plaster.
Traces of plaster and wrought nails are all
that remain of the original coffering beneath
the tambour. Some of the brightly glazed
earthenware petals fixed with wire to the
moulding have been preserved. The dome
was protected from the elements outside by
a coat of render. Rainwater was guided away
with great efficiency, and yet out of sight, by
an intricate system of channels in the form of
deep cracks in the wall, ledges and canopies.
Nicolas de Pigage lent the ruins an extremely
idiosyncratic plan and cubature. The three
identical concave access walls deprive
the building of an orientation. The upper
storeys that rise in a cylinder reinforce
the impression that the structure keeps
turning away. Irregular, apparently arbitrary
cracking, fracturing, crumbling and deep
wells of erosion dissolve the contours of the
structure and make it difficult for visitors
to grasp its true shape. On closer analysis,
one can tell that the entire building respects
a sophisticated pattern of measurements,
each module a fathom. Each section develops
geometrically from the last, conserving a
proportionate relationship.
Above all, however, the masterful skills
of Nicolas de Pigage are demonstrated by
the split round temple of the crown. The
dome’s shape is only that of a horseshoe
so the tensile ring around its base, the key
element in a dome-supporting structure, is
missing. Nevertheless, the dome remains
essentially unchanged until today. Extensive
investigations have revealed the solution
contrived by Nicolas de Pigage. Wroughtiron
posts were embedded within five of
the belvedere’s six pillars, and together
with crosspieces made of iron profiles these
ensured resistance to any bending in the bed
joints of the masonry. These vertical iron rods
are linked at a height of 15.40 m to the first
of the open circular beams which, below the
cornice, to some extent bind the three-quarter
circle at the base of the dome. A second open
ring at a height of 16.45 m follows a groove in
the moulding. It is both clasped to the pillars
and locked into an impost at each end. If the
anchor were to be placed under strain, the
conical, concentrically formed posts would
be pulled taught. In this manner, the beams
and imposts create a stable open girdle able to
absorb the forces in the dome. What we find
in the Temple of Mercury is a predecessor of
pre-stressed structural design.