Civil Engineering Reference
In-Depth Information
the blocks leaving the roughly jointed tails and rubble interior of the wall to be set
in mud mortar (cf the analagous question of
opus incertum
and
opus reticulatum
).
However there is virtually no discussion of this question in manuals or reports.
Nonetheless in one connection there is both ancient discussion and surviv-
ing evidence of the use of gypsum based mortar in ancient stone masonry. h e
Greek philosopher h eophrastus (Aristotle's successor as head of the Lyceum)
wrote a treatise on stones (
Peri ton Lithon
—ca 300 BC) wherein he notes that a
highly cementitious substance was prepared from gypsum which could be used to
cement other materials together. In particular it was used as a mortar so strong
that the blocks of stone would break apart before the mortar joint would fail.
What h eophrastus was evidencing here is most likely the masonry of city walls, a
special case where normal considerations of economy took second place to human
survival against siege warfare—cf the walls of Tyre which resisted Alexander's bat-
tery for so long (Arrian,
Anabasis
2, 21, 4). Evidence of the use of gypsum in this
connection exists in the contemporary circuit walls of Dura Europas, where the
blocks, both dressed facing blocks and core rubble are i xed with gypsum mortar
(J.-P. Adam,
La Construction Romaine
, pp. 59, 69; J.-C. Bessac & P. Leriche, “Les
Dossiers d'Archéologie,” 171, 1992, pp. 70-81).
h is subject in general is inadequately investigated.
Fixation
of blocks,
in dressed
stone ma-
sonry by
cramping
& dowel-
ling
(ii) Inset coupling between blocks (cramping and dowelling)
h e practice of i xing blocks of masonry in place by dowelling and cramping is
the counterpart (i.e. is inverse in its application) to that of i xing by cementitious
mortar. Whereas the latter is used with roughly jointed or rubble masonry, the
former is used with i nely dressed stone masonry (“dimension stone” blocks) set
dry jointed. h e practice thus has a limited usage in the ancient world. To all
intents it is limited to Pharaonic Egyptian masonry and Classical Ashlar masonry.
h us it does not occur in small block “bastard ashlar”, e.g. Zoser masonry. h is
is a matter of some pragmatic importance, since it serves to identify mortises for
dowels in the upper bed joints of bastard ashlar, not as evidence of dowelling for
another course of such masonry, but as arrangements for anchoring timber beams
used as re-inforcing for a superstructure of a dif erent type of masonry, e.g. mud
brick or rubble.
h e device of cramping together blocks of i nely dressed masonry is of consider-
able interest in the history of building technology. Its history extends over the entire
period of building in i nely dressed masonry in the ancient world and it appears to
bring into focus general issues. Cramps occur with the earliest Egyptian Pharaonic
masonry (ca 2500 BC) as in the earliest classical Greek ashlar construction (ca 600
BC). h e device thus constitutes one feature in Classical Greek building which is
patently derived from Egypt—although the precise mechanics of the dif usion are
