A Revolutionary Carbon-Dating Study of Ancient Jerusalem
The job of an archaeologist revolves around answering a short question. When was it made? This question is answered using several methods. The more precise the dating method, the more accurately the question can be answered.
For more than a century, the most common (and accurate) method of dating a discovery revolved around ancient pottery. Pottery styles change over time, which means certain styles can be associated with specific time periods. By dating a specific piece of pottery, archaeologists can often date the layer, including any other finds that might be found in it, to the same period as the pottery.
While assigning a date using pottery has proved effective, it isn’t perfect. And it’s not rare for the dates assigned to certain pottery types to be debated. For this reason, it is beneficial to have other dating methods. Over the last two decades, carbon-dating has emerged as an especially helpful tool.
In this article, we will consider a new landmark study of ancient Jerusalem. Thanks to new carbon-dating samples, we now have a more complete picture of Jerusalem’s building program during the time of Israel’s biblical kings.
The study, published on April 29 in the pnas journal, is titled “Radiocarbon Chronology of Iron Age Jerusalem Reveals Calibration Offsets and Architectural Developments.” In the study, 103 carbon samples were taken from Iron Age layers (1200–586 b.c.e.) at several locations in ancient Jerusalem, also known as the City of David. What did the new study reveal?
A Well-Inhabited City
For more than two decades, the fiercest debate in archaeology has centered on the reliability of the history of the united monarchy of kings David and Solomon as documented in the Bible. In the exhibit edition of Let the Stones Speak (free upon request), we note the abundance of evidence from excavations across Israel supporting the biblical account. These include monumental buildings, discovered by the late Hebrew University archaeologist Dr. Eilat Mazar, on the ridge of ancient Jerusalem.
Unfortunately, there is an abnormal amount of debate about the dating of these buildings, with some archaeologists dating them to the ninth century b.c.e., roughly 100 years after King David. Although the recent radiocarbon study did not include samples of sites on top of the ridge, it did produce evidence indicating the widespread habitation of Jerusalem during the time of David and Solomon.
Of the 103 carbon samples (mainly seeds) from Jerusalem, 18 of them (almost 20 percent) fell within the early Iron Age (12th to 10th century b.c.e.). Only three of these samples were found in the context of early Iron Age pottery; the rest were found inside later building materials such as mortar. This “clearly indicates widespread occupation of yet undetermined character, often underestimated due to the limited architectural contexts attributed to this period,” stated the report.
Although the study cannot reveal the nature of Jerusalem’s construction in the 10th century, it does reveal that the city was densely inhabited at that time. According to Prof. Elisabetta Boaretto, one of the main authors, the number of samples from this period is statistically significant and cannot be ignored. “If there was just a very meager occupation, the hypothesis that ‘old seeds’ just ended up in later construction materials is not sustainable,” Boaretto told Haaretz. “You would not find that many dates spread all over the site—20 percent of the sample is a lot” (“Jerusalem in King David’s Time Was Much Larger Than Previously Thought, Researchers Say,” April 29).
https://www.youtube.com/watch?v=-QgJphw7Vfg
Prof. Yuval Gadot, from Tel Aviv University, participated in the study and agreed with Professor Boaretto. (Gadot is also the codirector of the Givati Parking Lot excavation in the City of David and has years of experience with the site.) “It’s true,” he told Haaretz, “I can’t tell you what they built in this period, and who built it, but this material had to come from somewhere; someone was active there.”
Professor Gadot is not a biblical maximalist. In fact, on the topic of David, Solomon and Jerusalem, he has long been closer to the minimalist camp. However, his opinion is shifting, thanks to the evidence being furnished in his excavation and from this new study. “If my pendulum has to move somewhere, it now goes more in the direction of the city than the village because of these results,” he said. Kudos to Professor Gadot for following the science.
Ninth-Century Westward Expansion
Another debate revolves around the dating of Jerusalem’s westward expansion. A historical reconstruction based on the Bible places King David’s Jerusalem on the lower portion of the eastern hill (2 Samuel 5:7-9). King Solomon then expanded the city northward, onto an area known as the Ophel (1 Kings 3:1). Then, as attested to by earlier archaeological excavations, the much larger western hill was inhabited at least by the middle of the eighth century b.c.e. and was fortified with walls by the time of King Hezekiah in the late eighth century b.c.e.
But how soon after the 10th century did Jerusalem start expanding onto the western hill? Did it only begin during the reign of King Hezekiah, or was it earlier?
This new study provided an answer: Carbon-dating shows it occurred in the first half of the ninth century b.c.e., which is much earlier than initially thought.
A monumental building (Building 100) from the First Temple Period sits at the center of the Givati Parking Lot excavation. This structure gives us the earliest insight into the westward expansion. According to the carbon-dating study, the building underwent several renovations throughout its 300 years of use. Carbon samples found underneath and in the first phase of the building’s construction show that it was constructed between 900 and 850 b.c.e.
Furthermore, there is evidence of widespread terracing of the bedrock, perhaps in preparation for the construction of Building 100. Put together, the authors now believe that the “city expanded westward in the ninth century b.c.e., and possibly earlier.” If it was earlier, as the authors allow, this would put the expansion as early as the end of the 10th century—very soon after the reign of King Solomon.
Consider this logically: If Jerusalem was expanding in the late 10th and early ninth century, then the top of the ridge—the original ancient core—would have been inhabited before this time (any expansion would have first had to occur north, before moving west). This is a significant development in the discussion about Jerusalem. Until recently, the late Dr. Mazar stood virtually alone in her belief that the construction on top of the ridge occurred in the 10th century.
The biblical text doesn’t explicitly reveal which biblical king was responsible for Jerusalem’s early expansion. In the press release about the study, Professor Gadot suggests the expansion likely occurred during the reign of King Jehoash, in the late ninth century.
However, looking at the dating of the study itself, King Asa of Judah, who reigned from 911 to 870 b.c.e., is perhaps a better candidate. The Bible records that his reign marked a period of stability and peace, both of which would be conducive to massive construction projects adjacent west of the core city.
Although Jerusalem is not mentioned specifically, the Bible does speak more generally to Asa’s large-scale building activities: “And he built fortified cities in Judah; for the land was quiet, and he had no war in those years; because the Lord had given him rest. For he said unto Judah: ‘Let us build these cities, and make about them walls, and towers, gates, and bars; the land is yet before us, because we have sought the Lord our God; we have sought Him, and He hath given us rest on every side.’ So they built and prospered” (2 Chronicles 14:5-6).
We know that Israel enjoyed 40 years of peace under Solomon, which allowed for the expansion of Jerusalem northward onto the Ophel. Perhaps the 30 years of peace during King Asa’s reign, which began only four decades after Solomon, allowed for Jerusalem’s westward expansion.
Regardless of which king is responsible, the fact that Jerusalem expanded in the ninth century proves that the core Jerusalem was a bustling, well-developed city earlier than previously thought.
The ‘Old-House Effect’ Is Real
When attempting to date structures in Jerusalem it is important to understand the “old-house effect,” a phenomenon that has only been strengthened by the new study.
Typically, archaeologists date the construction of buildings by analyzing the material remains uncovered in the earliest floor of the structure. By dating the material remains on top of the floor and directly underneath it, a window of time is created identifying the date of construction. Most often, the material on top of the floor is sealed by destruction, thus giving the latest possible construction date and end-of-use for the structure.
Generally, this method of dating is accurate, but only if the building was in use for a few decades before it was destroyed. What if the building was in use for hundreds of years before it was destroyed? This is the pitfall of the old-house effect: A structure could have existed for centuries, but most finds will only relate to its destruction.
In Jerusalem, there are no destruction events between King David in the 10th century b.c.e. and the Prophet Jeremiah in the sixth century, save for the eighth-century earthquake (to be addressed later). Therefore, the archaeological remains appear to favor a later date for construction. Yet in reality, the structures were built much earlier. As such, the projects of the earlier builders (such as David and Solomon) are harder to delineate.
Building 100 is a perfect case study to prove that the “old-house effect” is real in Jerusalem. Those who have followed the Givati excavation are likely already familiar with some of the reported Iron Age finds. These include several crushed storage vessels that stored vanilla-laced wine; the seal impression of Nathan-Melech, a royal official mentioned in the book of Kings; as well as hundreds of ivory inlay fragments. All of these discoveries date to the decades before the final destruction of the building. However, because of the old-house effect, they do not represent the building’s entire period of use.
Thanks to this groundbreaking radiocarbon study, we now have a much clearer understanding of this site.
First, we now know that Building 100 was first built in the early ninth century b.c.e. Then sometime during the middle of the eighth century it underwent a large renovation, which Professor Gadot and his colleagues posit was a result of the cataclysmic earthquake mentioned in Amos 1:1. Gadot and colleagues were able to date the reconstruction following the earthquake by carbon dating a dead bat found in a recess in the building. A second renovation occurred between 680 and 670 b.c.e. when a second floor was added. Finally, the whole building was destroyed in 586 b.c.e.
“Remarkably, while our radiocarbon determinations demonstrate [an approximate] 300-year use of Building 100, the pottery found in association with the building belongs almost entirely to the end of the seventh to the early sixth centuries b.c.e., in the terminal Iron Age,” the authors write in the study.
Archaeologists must take the “old-house effect” into account when reconstructing Jerusalem’s history based on the archaeological remains. Doing so shows that many buildings were constructed much earlier than we might otherwise accept.
Added to that, Jerusalem’s old-house problem is another indication of the stability Jerusalem experienced through the period of the biblical kings. As the authors note, “The lengthy period of use of Building 100, determined from our radiocarbon dates, may be emblematic of the city’s long-term economic flourishing and relative political stability up until the Babylonian invasion at the beginning of the sixth century b.c.e. The city’s continuous occupation indicates a time of demographic growth while recurring conflicts with regional empires negatively affected settlements elsewhere in the region.” In other words, Jerusalem survived unscathed from the time of David for a period of almost 400 years, whereas other cities in the region were often conquered and reconquered.
The Bible credits God for this protection in numerous passages. The greatest example of this occurred when the mighty Assyrian Empire conquered all the cities of Judah except Jerusalem during the reign of King Hezekiah. As the Prophet Isaiah recorded at the time, God promised: “I will defend this city to save it, for Mine own sake, and for My servant David’s sake” (Isaiah 37:35).
Calibrating Science With the Bible
On the eastern side of the City of David ridge, scientists took radiocarbon samples from the area just above the Gihon Spring (Area U). Here, 11 separate floors have been found, all built on top of each other. These floors have been dated from the eighth century to the sixth century b.c.e. These two centuries fall inside what is known in the carbon-dating world as the Hallstatt Plateau, a period in which the ratio of carbon 14 to carbon 12 in the atmosphere is known to be inconsistent. This makes it extremely hard to rely on (and trust) carbon dates in this window as a precise dating tool.
To ensure accurate results, carbon dates in this period especially must first be calibrated using an object or layer of known date. Without calibration, carbon dating cannot stand alone as a reliable dating method.
Most of the time, tree rings (which typically grow at a rate of one ring per year) are used to calibrate the carbon dating curve. For example, a carbon sample taken from a tree ring from 3,000 years ago, might return a date 2,900 years ago. In which case, the tree ring date is considered true (the object of known date) and all other carbon dates that return a value of 2,900 years ago will be calibrated back 100 years.
However, the problem with this is that there are often differences between the amount of carbon 14 in the atmosphere in one location of the globe compared to the amount of carbon 14 in the atmosphere at the location of the trees used to calibrate the curve. In this case, calibrating the carbon dates locally allows for a more precise result.
This is exactly what happened in Area U of the City of David.
The local events used to calibrate the carbon dates are biblical events. That’s right: Two biblical events have been so well documented and proved, even by other historical sources and methods, that they are considered more reliable than tree rings.
In the case of Area U, organic samples were taken from the 11 floors along with pottery. The earliest of these floors is related to the large earthquake from the time of Amos and is known to many other archaeological sites throughout Israel. The earthquake dates to approximately 760 b.c.e., and thus the carbon samples taken from this layer were calibrated to this biblical event.
The destruction of the latest floor, dated by its pottery in connection to the biblical text and Babylonian chronicle, dates to around 586 b.c.e. The carbon dates found in that destruction were calibrated to that biblical event.
This is incredible! These two events, documented in the biblical text more than 2,500 years ago, are considered so reliable (down to the specific year) they were used to synthesize the scientific data. In this case, the curve was calibrated by the Bible! Those biblical events were also corroborated by previous finds from other empires, providing further evidence for the reliability of Scripture. (As an aside, the archaeologists noted that the earthquake layer related to a nearby city wall, which was thought to have been built by King Hezekiah. Now they know it was likely built by King Uzziah, a known builder of Jerusalem—2 Chronicles 26:9.)
By recalibrating the curve using these two biblical events, scientists revealed a huge shift in the amount of carbon 14 in the atmosphere from 730 to 710 b.c.e. This shift was already reflected in worldwide calibration data. However, the study showed that there was an even greater carbon-14 enrichment taking place locally in the land of Israel than elsewhere.
In the future, this more precise carbon-14 chronology gained by the 11 consecutive floors might yield one of the most important results of the City of David radiocarbon study. These two dates allowed the researchers to more accurately provide regional calibration data for other samples in the intervening floors. The researchers were then able to give more accurate dates to the pottery styles found inside each layer, which can now be used to further refine dating of other sites in Israel featuring those same pottery styles. Thus, the knowledge gained from this study—which combined archaeological stratigraphy, radiocarbon samples and the biblical text—is making possible more accurate dating of future discoveries in the late Iron Age.
Welcome to biblical archaeology in the 21st century! Prof. Yosef Garfinkel, director of the Khirbet Qeiyafa excavation, once remarked that the most important discovery of his excavation was the humble carbon samples—the olive pits. Without them, he would not have had the dating tools to confirm an early 10th-century b.c.e. date for the site. Archaeologists were then able to use the pottery found at Qeiyafa (dated by the short-lived carbon samples) as a key to the dating of their own sites to the 10th century.
This new Jerusalem radiocarbon study can function as a similar all-important key for other sites from the eighth to sixth century b.c.e.
Thanks to this study, we can say with much greater confidence that Jerusalem at the time of David and Solomon was more a city than a village, as the minimalists claim. This study also supports the old-house effect in Jerusalem.
Beyond these two crucial developments, this new study also gives archaeologists the ability to refine their dating of archaeological remains all across Israel!
Congratulations to the devoted team of researchers for their painstaking efforts over the past few years to conduct this landmark carbon-dating study! Thanks to their efforts, archaeologists excavating Jerusalem now and in the future will find it easier to answer the question—when was it made?