Earth_Magazine_October_2017

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erusalem is one of the oldest cities
in the world, dating back to at
least 2400 B.C. Downhill from the
heart of the city is Gihon Spring, a
year-round natural fount that was
likely the primary water source for the
ancient city. Defensive fortifications built
around the spring, known as the Spring
Tower, were originally dated to the Mid-
dle Bronze Age, around 1700 B.C., but a
new study reveals the tower could be as
much as 1,000 years younger.
Jerusalem, located between the Dead
Sea to the east and the Mediterranean
Sea to the west, has had a tumultuous
past, with the land long-contested on
political and religious grounds. The city
has been destroyed at least twice, besieged
dozens of times and continuously rebuilt,

creating many layers of history, the

chronology of which can be difficult to

pin down. Few studies have been done

to determine absolute ages for buildings

and other features in the city. “Jerusalem

has been excavated many times, but the

number of absolute radiocarbon dates

we have for structures in the city can

be counted on one hand,” says Elisa-

betta Boaretto, a nuclear physicist at the

Weizmann Institute of Science in Israel

and an author of the new study, published

in the journal Radiocarbon.

As part of ongoing preservation and

resealing of the Spring Tower, Boaretto

and colleagues studied layers of sedi-

ments under the massive boulders that

make up the 7-meter-thick base of the

tower. The boulders themselves did

not provide any datable samples,

Boaretto says. “But underneath the

boulders, the soil exhibits layering

typical of archaeological strata, and

these can reveal the latest date that

the site was occupied before the

tower was built.”

After carefully identifying and

mapping the strata under the boul-

ders, the team sifted microscopic

bits of organic material from the

layers for radiocarbon testing. The

radiocarbon dates for the top layers

of sediments, just under the boul-

ders, revealed a surprise: Rather

than dating to about 1700 B.C., the

top layers were deposited between

900 and 800 B.C., suggesting the

tower was constructed during the

Iron Age.

“Instead of the Middle Bronze

Age, we got a nice stratigraphic

sequence that ended in the 9th

century B.C., much later than we

expected,” Boaretto says. Previ-

ously, the age of the tower had been

established by dating fragments of

ceramics found in the fill between

boulders in the tower. But the fill

used to build the tower may have

been significantly older than the

structure itself, Boaretto says.

The new study was “very meticulously

done,” says David Ussishkin, an archae-

ologist at Tel Aviv University in Israel,

who was not involved in the study. The

new dates do not prove exactly when the

tower was built, but rather set a maxi-

mum age for it. “The carbon dates say

9th century, but they are dating the layers

beneath the foundation of the building.

The building could have been built later,

during the 8th century.”

The new dating affects the historical

timeline for construction of the city’s

walls and other fortifications, Boaretto

says. “By changing the construction date

of the tower, you change everything

else that is related archaeologically and

stratigraphically. It’s something of a dom-

ino effect.”

Ussishkin says he thinks the fortifica-

tions were built in the 8th century, well

after the reign of King Solomon. “There

is some resistance to this idea, that there

were no fortifications at the time of King

Solomon,” he says. “But this tower was

not isolated, standing there by itself. It’s

part of the fortifications of the city. If

the tower was built later, then the forti-

fications must have been built later too.”

Mary Caperton Morton

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