Grōma
The measuring instrument used by land-surveyors, who were from it called
gromatici. See
Agrimensores.
The groma is represented on the gravestone of a
gromaticus found some
years ago at Ivrea (Rossi,
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Groma. (From a gravestone at Ivrea.)
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Groma e Squadro, 1877, p. 43). The design is not in perspective, but, if
allowances be made for the inexperience of the artist, it explains fairly well the nature of
the instrument. Two small planks crossing one another at right angles are supported on a
column or post (
ferramentum). Plummets (probably four, though there are
only two in the monument) are suspended from the planks to guide the operator in securing a
vertical position of the column, and a horizontal for the cross-pieces. The small circles at
the point of section in the drawing may represent a hole in the continuation of the column for
the operator to look through, or a large hole in the cross-pieces to allow of their
being tipped up to a certain angle if necessary. The latter is the more likely, for in that
case the continuation of the column would serve as a support to prevent the cross from
falling. In any case it obstructs the view along the planks.
The use of the instrument is obvious. It is intended to guide a surveyor in drawing real or
imaginary lines at right angles to one another, more especially in fixing the
cardo (or north and south line) and
decumanus (or east and west
line) essential to the orientation of any
templum or to the laying out of
a Roman camp. See
Castra.
