When the Romans finally overcame the besieged Jewish citadel of Masada
in AD 73, they made their way into the city along a ramp made from the wood
of the tamarisk tree. That piece of wood has now provided evidence that
supports contemporary reports of a thriving agriculture in a region that
has become desert.
Flavius Josephus, the Jewish historian who wrote in the first century
AD, noted that when King Herod built the mountain fortress at Masada on
the shores of the Dead Sea, he reserved the top of the hill for cultivation.
Josephus also relates that when Herod’s brother, Joseph, was hiding
at Masada he almost died of thirst, but was saved by a rainstorm. Today
rain comes only once every few years and the extremely arid climate makes
Now a team of Israeli scientists has discovered chemical evidence that
the climate may have been wetter two thousand years ago – bearing out Josephus’s
description of the place.
Dan Yakir of the Weizmann Institute of Science at Rehovot, and his colleagues
Joel Gat and Arie Issar of Ben Gurion University of the Negev and others,
analysed the concentrations of stable isotopes of carbon and oxygen in the
cellulose of the Roman ramp. The proportions of different isotopes vary
according to the conditions in which the trees grew.
Tamarisk trees are characteristic of the Masada region, and the researchers
presume that Roman soldiers cut the wood locally. The researchers analysed
samples of tamarisk wood from the ramp, unchanged since the Romans defeated
the last of the Jewish rebels who had fled to Masada. For comparison, they
sampled wood from modern tamarisks from the area around Masada and from
trees growing in central Israel, where the climate is Mediterranean.
The ancient cellulose was found to contain low concentrations of two
stable isotopes, carbon-13 and oxygen-18. Samples from the modern wood –
from both sites – had higher concentrations of these two isotopes. Plants
that grow under stressful conditions – in drought-prone regions or in salty
soil – tend to have high concentrations of carbon-13. Higher levels of oxygen-18
are associated with low humidity. So the measurements provide two independent
indications that Masada’s climate in the 1st century AD was less harsh
and more amenable to agriculture than it is today.
The researchers point out that this type of isotope analysis can be
a valuable tool for interpreting historical events in areas on the desert
margins, where even small variations in climate can be enough to produce
major changes in vegetation – and make the difference between a land that
is habitable or uninhabitable.
Archaeological excavations, including that at Masada, have shown in
the past that Josephus’s history of the Jewish nation in the Roman period
is generally accurate. Yakir’s study provides chemical confirmation of his
reliability as a reporter. ‘It was a very clever idea to study the trees
from the Masada site,’ says Yehouda Enzel, a palaeohydrologist from the
Institute of Earth Sciences at the Hebrew University of Jerusalem. ‘Although
there was already historical evidence that the climate was wetter, the
isotope study is more convincing’.