Environmental Engineering Reference
In-Depth Information
more because their construction, employing only hun-
dreds of lumbermen, quarrymen, carpenters, stonema-
sons, glassworkers, and haulers at a time, lasted scores of
years, even centuries. In contrast, Teotihuacan pyramids,
the largest such structures in the Americas (fig. 7.10),
needed much less energy because their cores were made
up of earth, rubble, and adobe bricks, and only the exte-
rior was faced with cut stone (Baldwin 1977). No other
single preindustrial structure embodied as much animate
energy as did Khufu's pyramid, but that total was easily
surpassed by two of the classical world's greatest engi-
neering networks, Rome's aqueducts (Van Deman 1934;
H. B. Evans 1994; Hodge 2002) and the Roman
Empire's system of roads (Pek´ry 1968; Chevalier 1976;
Sitwell 1981; Kolb 2001).
My calculations, based partly on assumptions detailed
in Blackman and Hodge (2001), indicate that the chan-
nels for Rome's 11 aqueducts (515 km), built between
312
B
.
C
.
E
. and 226
C
.
E
. and using nearly 6 m
3
of stone
per meter of the conduit, required as much stone as did
Khufu's pyramid. To this must be added stones for about
58 km of elevated arches, and the volume of soil and
rock that had to be removed for the sloping aqueduct
ditches clearly surpassed the total volume of stone used
to build water channels. Understandably, Pliny in his
Historia Naturalis (book 36), wrote that ''there was
never any design in the whole world . . . more admirable
than this,'' and Frontinus, in his detailed treatise on the
city's aqueducts, displays the pride of a practical engineer
(and a Roman) by imploring his readers to compare
these structures with ''the idle pyramids, or else the indo-
lent but famous works of the Greeks.'' Some Roman
aqueducts had a much higher energy cost because of
large amounts of lead needed for high-pressure siphon
pipes that were used to cross river valleys; siphons in the
Lyon water supply needed about 15,000 t of the metal
(Hodge 1985).
Principal Roman highways were 12 m wide, country
roads less than 3 m (Forbes 1965). If one assumes, con-
servatively, an average width of 6 m and a depth of 1 m
for all hard-surface Roman trunk roads (85,000 km by
300
C
.
E
.), these roads would have required the emplace-
ment of no less than 500 million m
3
of stone for the base
and the top summa crusta as well as gravel, sand, and
lime after first moving some 750 million m
3
of earth
and rock for the roadbed and agger. An earthen embank-
ment, the agger often measured up to 1.8 m above its
surroundings and up to 12 m wide. With about 0.5 m
3
of stone and gravel and 5 m
3
of soil handled per capita
per day, the tasks of quarrying, cutting, crushing, and
moving stones and gravel, fashioning embankments,
preparing concrete and mortar, and laying the road
required on the order of 1 billion labor days, or 2.5 PJ
of embodied energy.
7.5 Transportation: Roads and Ships
Preindustrial land transport was dominated by draft ani-
mals, and its capabilities depended not only on the kind,
size, and health of commonly used species but also on
the ability to reduce friction, that is, on the quality of
roads and vehicles. Wheels varied from heavy, segmented
solid disks fixed to a rotating axle (still in use in parts of
Asia until the twentieth century) to light, multispoked
arrangements that rotated on a fixed axle. The front axle
itself was either pivoted (in ancient Persia, Celtic Europe)
or fixed (during the Roman era). Roads ranged from
muddy ruts and sandy trails to hard-top viae, and in
many parts of the Old World their quality had greatly
declined during the Middle Ages and improved only dur-
ing the nineteenth century. On a smooth, hard, dry road
