Bronze Age Research Paper

We present the excavation of a grave at Mahtoutabad, near Konar Sandal South, Kerman, Iran, one of the protohistoric cemeteries plundered in the Jiroft area since 2001. This grave, at present, is the only scientifically excavated and... more

We present the excavation of a grave at Mahtoutabad, near Konar Sandal South, Kerman, Iran, one of the protohistoric cemeteries plundered in the Jiroft area since 2001. This grave, at present, is the only scientifically excavated and published burial of the Bronze Age urban civilization of the Halil Rud valley, famous for the outstanding quality of its looted chlorite artefacts. Among the furnishings of the grave were animal bones and food offerings, ceramics, and stone and copper items. The objects set the grave in a coherent cultural and chronological framework, around 2400-2200 BC. Micro-stratigraphic recording provided information on the funerary practices. These latter included notably the consumption of the meat of an ovicaprine. As different parts of the animal were found in different locations of the stratified mortuary structure, the feast can be synchronized with different steps of the funeral and burial processes. A reopening of the grave, for shifting part of the skeleton to a different, secondary burial, remains unexplained. Considering the effects of a wide range of post-depositional processes, we explore possible symbolic implications of the grave's spatial patterns.

In the discussion that follows, we present the results of the radiocarbon dating in chronological order for the Augsburg region. We bring them together with the traditional archaeological division of the respective phases in order to connect traditional relative-chronological phases with the absolute-chronological evidence. These results are then compared with the old and new dates from Singen.

Augsburg Region

The earliest dates for graves of the BBP in the Augsburg region start with their 2σ calibrated range already in the 25th century BC–e.g. Königsbrunn, Ampack gr. 1: 2478–2339 BC (94.4% probability) and 2317–2310 BC (1.0% probability); Augsburg, Hugo-Eckener-Str. gr. 5: double grave, combined calibration of both burials: 2469–2310 BC (95.4% probability) (Table 2). The three latest dates for BBP graves derive from the cemetery Hugo-Eckener-Str. (graves 1, 9 and 10) and are almost identical in their dating with the latest 2σ calibrated time span ending in 2039 BC (grave 1). All the other dates for BBP graves are evenly distributed between the oldest and the youngest date (Fig 3). The sequence of clusters of BBP dates in Fig 3 does not correspond with any archaeological division of the BBP, but only results from a sequence of small plateaus of the calibration curve.

At first, it seems difficult to decide whether there is a significant overlap between the latest BBP and the earliest EBA burials. If one supposes that the three latest BBP burials were buried at almost the same time (the three related uncalibrated dates fall within a range of seven years: 3748–3741 14C BP), one can calculate a combined calibrated age, which significantly narrows the time range with the highest probability: 2201–2133 BC (93.0% probability) and 2076–2064 BC (2.4% probability). This indicates that the last BBP burials in the Augsburg region were most probably not laid down after the early second half of the 22nd century (Fig 4).

The oldest EBA dates all derive from the cemetery Haunstetten, Postillonstraße, namely graves 4, 5 and 14 (the three related uncalibrated dates fall within a range of 20 years: 3717–3697 14C BP). The narrow time range of their deposition makes it possible to calculate a combined calibrated age. The 2σ calibrated range spans 2141–2112 BC (22.8% probability) and 2103–2036 BC (72.6% probability) BC.

Calculating the overlap of the two phases (BBP and EBA) using a multi-phase model in Oxcal v4.2.24 [36] with IntCal13 [37] strengthens the argument of a sequence (Fig 5). Modeled values of “Boundary End 1” (end of BBP) and “Boundary Start 2” (beginning of EBA) do not overlap more than 20 years.

Therefore, one can assume that there is hardly any overlap or no overlap at all between the latest BBP and the earliest EBA burials. At least in the Augsburg region, there is definitely no indication for either a substantial overlap or a hiatus between both periods. The data suggest a continuous and fluent sequence from the BBP to the EBA.

The new dates also help to better understand the development of the EBA itself. We are able to connect the traditional division of Bz A into the sub-phases Bz A1 and A2 with absolute dates for the respective type objects. Ruckdeschel defined the following pin types as type objects for Bz A1 (with its sub-phases Bz A1a and Bz A1b) and Bz A2 (with its sub-phases Bz A2a, Bz A2b and Bz A2c) [15] (see below):

  1. Bz A1a: Ruderkopfnadeln (with large or small head), bone pins and boar tusk pins
  2. Bz A1a–A1b: Scheibenkopfnadeln
  3. Bz A1b: Schleifenkopfnadeln and Horkheimer Nadeln.
  4. Bz A2a: Ösenkopfnadel, Hülsenkopfnadel and schräg durchlochte Kugelkopfnadel.

We were not able to date graves with Bz A2b and Bz A2c type objects, which are very rare in southern Germany (cf. [17]). The Lochhalsnadel type Paarstadl was dated by Ruckdeschel to Bz A2c, but it has meanwhile been dated to the beginning of the Middle Bronze Age (Bz B) by other authors [45], [17]. We agree with the Bz B date for this type of pin, also because the specimen dated by us was associated with a most characteristic Bz B dagger in one of the burials (Oberottmarshausen gr. 5). Therefore, we see the following pin types from our grave inventories as characteristic of Bz B: Lochhalsnadel type Paarstadl and Dreiringnadel type Muschenheim. Rollenkopfnadeln mit tordiertem Schaft start in Bz B, but continue well into the later MBA [46].

We could date altogether 36 graves with Bz A1 pins, three graves with Bz A2 pins and five graves with MBA pin types (Fig 6).

Fig 6. Plot of all pins with radiocarbon dates from Singen and the Augsburg region.

Pin types with more than two dates are supplemented with a sum calibration (black) to show their overall timespan.

https://doi.org/10.1371/journal.pone.0139705.g006

Graves with Bz A1a pins are among the oldest EBA graves analyzed within our project (Haunstetten, Postillonstr. gr. 14). Several 2σ calibrated ranges start shortly after 2200 BC, but the 2σ calibrated range of most of these graves spans the second half of the 21st century and the complete 20th century BC. Therefore, we propose a period of deposition of these pins from ca 2150/2100 BC until 1900 BC for the Augsburg region. The 2σ calibrated ranges of the two type objects of Bz A1b start in the late 21st century BC (Wehringen, Hochfeld grave 7: 2030–1916 BC with 95.4% probability). However, these pin types have a much longer period of use and were still deposited after 1900 BC and probably even until 1700 BC (e.g. Kleinaitingen, Gewerbegebiet Nord grave 10: 1883–1736 BC with 87.5% probability and 1716–1695 BC with 7.9% probability). It is clear that Bz A1a and Bz A1b are contemporaneous for around 150 years. Taken together, Bz A1 can be dated in the Augsburg region to the centuries between 2150/2100 and 1750/1700 BC.

The three dates with classical Bz A2 pin types (i.e. Bz A2a in the Ruckdeschel system)–all from Kleinaitingen–were extremely similar with almost the same uncalibrated dates and indicate a deposition between ca 1900 BC and the years around 1700 BC. Compared with the Bz A1 dates, it seems that Bz A2 pins were worn and deposited contemporaneously with Bz A1b pins, whereas Bz A1a pins could have been replaced by Bz A2 types (Fig 7).

The oldest burial with type objects of Bz B (the first phase of the MBA) is Oberottmarshausen, grave 5 (1744–1598 BC with 84.0% probability and 1586–1533 BC with 11.4%probability). It contains a Lochhalsnadel type Paarstadl and a dagger with trapezoid hilt (i.e. [47]: series K34 or Q60). Therefore, it is most probable that the deposition of clear Bz B type objects started already in the 17th century BC in the Augsburg region. The other grave with a Bz B pin type, i.e. Oberottmarshausen grave 18, dates to the 17th or 16th century BC. However, the small number of graves with Bz B type objects does not allow further insights into the chronological position and duration of Bz B. Unfortunately, the Rollenkopfnadeln mit tordiertem Schaft are not of typological significance, as they start in Bz B (and in Switzerland even late in Bz A2; cf. [46]) and continue further into the MBA.

Considerations about the absolute dating of relative chronological phases and periods of depositions of diagnostic artifacts need to consider reservoir effects, which may have shifted the radiocarbon ages by several hundred years (Table 3). Overall, the 14C data of the bone collagen of the BBP burials and especially those who were associated with certain EBA pin types appear comparatively consistent [48], [49]. They lack outliers towards older dates, which may have been caused by remarkable consumption of marine or freshwater food sources. This is in agreement with the stable carbon and nitrogen isotope ratios of bone collagen (Table 2). Despite the proximity of the Lech and Wertach Rivers, the δ13C values of between -21.3 and -19.8 ‰ and δ15N values of between 8.7 and 10.8 ‰ point to a predominance of terrestrial food sources, including crops as well as meat and dairy products of domestic animals. As to be expected for the inland location of the study area, there is no indication of any contribution of marine food sources. The data are also largely in agreement with previously investigated Final Neolithic to Early Bronze Age burials from southern Bavaria for which fish consumption was essentially excluded [50], [51]. Fig 8A illustrates the wide overlaps of the δ13C data of individuals of the BBP and those buried with diagnostic EBA pins (Fig 8). There is no correlation between old 14C ages and high δ15N or low δ13C values, which would indicate freshwater fish consumption [52]. The δ15N values of the individuals of the EBA shown in Fig 8B are more variable (range: 8.8–10.7 ‰) than those of the BBP which concentrate between comparatively low values of 8.7 and 10.0 ‰ (Fig 8). This pattern indicates that the older radiocarbon ages of the BBP burials are indeed due to their earlier calendaric age instead of resulting from extensive freshwater fish consumption. The light stable isotope ratios and 14C ages of the individuals buried with diagnostic Bz A1a and A1b pins overlap widely. Apparently independent of the 14C ages and grave goods, the δ15N and δ13C values tend to cluster by sites. Despite the very similar environmental conditions, this points to community-specific proportions of plant and animal-derived food and/or landuse and soil management, such as manuring [53], [54]. Overall, the light stable isotope ratios and the spread of the radiocarbon dates do not hint on possible overestimations of the periods of deposition of certain pin types due to different extents of reservoir effects among the investigated individuals.

Fig 8. Plot of the calibrated radiocarbon dates against the δ13C values (A) and δ15N (B) values of the same collagen extracts.

The letters indicate the burial sites: A: Königsbrunn "Ampack", H: Haunstetten "Hugo-Eckener-Strasse", O: Königsbrunn "Obere Kreuzstrasse", P: Haunstetten "Postillonsstrasse", U: Haunstetten "Unterer Talweg", W: Wehringen "Hochfeld". The C and N isotope data for Singen (S) are adopted from [42], [43].

https://doi.org/10.1371/journal.pone.0139705.g008

To conclude: at least for the Augsburg region, our data propose an absolute date for Bz A from 2150/2100 BC until at least 1700 BC. Bz A1a and Bz A2a pin types indeed represent a sequence (Fig 7). It seems that the so-called Bz A1b pin types are used during the complete EBA and cannot be used for any chronological subdivision. Compared with the traditional dating of Bz A between 2300/2200 BC and 1600/1550 BC, our results imply a substantial narrowing of the duration of the Early Bronze Age from 750/700 years to possibly 450 years. The MBA, however, seems to start already in the 17th century. Therefore, even if we have not been able to date graves with Bz A2b or Bz A2c type objects, there is not much time for a continuation of Bz A into the 17th century, unless one supposes a period of overlap between Bz A and Bz B.

The cemetery of Singen

Our (re-)evaluation of 10 graves from Singen revealed surprising results (Fig 9). The original dating of five graves (80, 7, 79, 74, 63) (Table 4) was confirmed in our study. The re-dating of grave 68 has to be considered with caution. Although the C:N ratio points to a good quality of the extracted collagen, the overall amount of carbon in the sample (4.7%) is rather low and there still is a chance that not all conservation chemicals have been removed. Most interestingly, the three earliest dates of the original series, i.e. graves 65, 70 and 19, shifted to a much younger date. The reason for this discrepancy remains unclear. It is possible that curators treated some of the bones immediately after the excavation and before the first sampling for 14C analysis. It should be noted that for radiometric 14C dating in the 1980ies rather large quantities of bone (50 grams and more) were required, which severely limits selective sampling to avoid contaminated bone. In contrast, the small sample size for AMS dating (typically 1 gram) allows for more rigorous sampling. In addition the ultrafiltration step in the AMS pretreatment sequence may have eliminated contamination more reliably. The observation that 5 out of 8 results agree well between the two techniques may in fact indicate the potential of contamination for the three older radiometric dates.

Our results force us to lower the starting point of the Singen cemetery from 2300 BC to 2200 BC at the earliest (with grave 63 as the oldest: 2200–2027 BC with 95.4% probability). It is even more likely that Singen rather started around 2150 BC (see sum calibration Fig 9). Excluding the unreliable result for grave 68, the latest 2σ calibrated ranges end around 1900 BC.

Comparison of Augsburg region, Singen and the Neckar region

Our new results from Singen fit very well to the results from the Augsburg region. The oldest dates from Singen (grave 63: 3712±12 14C BP) and the Augsburg region (Haunstetten, Postillonstraße, grave 5: 3717±23 14C BP) are almost identical as is the period of use of Singen and Haunstetten, Postillonstraße.

The dates for Bz A type objects from both regions provide a coherent view (Fig 6). The Ruderkopfnadeln (with small or large head) are identical in date and seem to have been used in both places at the same time. The much later date for Singen, grave 65, and the Ruderkopfnadel with large head from the grave fit perfectly to the time span for this type of pin from the Augsburg region. A difference can be seen in the early date for a Horkheimer Nadel from Singen, grave 79, which suggests a use of this type object in the 21st and possibly already in the late 22nd century BC, and, therefore, clearly earlier than in the Augsburg region. As the old dating of grave 79 was confirmed by the new measurement, the early position of this Horkheimer Nadel is beyond any doubt. Taking together the dating of the Horkheimer Nadel, shows a surprisingly long use of this particular type of pin, which spans a large part of the EBA.

Due to the lack of Bz A2 type objects at Singen, the cemetery does not allow further insights into the chronological sequence beyond Bz A1. However, Singen reconfirms the parallel existence of Bz A1a and Bz A1b.

The radiocarbon dates for the Neckar region around the city of Stuttgart (Fig 1) also match our results from Augsburg and Singen (Fig 10) [20]. Our new data show that the dates from the Neckar region do not contradict the chronological development as has long been assumed but fit very well into the overall picture.

There are only three graves with Bz A pins which were dated by the radiometric technique. In the Neckar region, two 14C dated graves contain Bz A1 type objects, i.e. a Scheibenkopfnadel or Ruderkopfnadel (Gäufelden, grave 1, individual 2; Remseck-Aldingen, Halden II, gr. 15); however, in both cases the state of preservation does not allow a further taxonomic identification of the pins which can, therefore, be attributed either to Bz A1a or Bz A1b following the Ruckdeschel system. The related 2σ calibrated ranges (Gäufelden, grave 1, individual 2: 1882–1747 BC with 95.4% probability; Remseck-Aldingen, Halden II, gr. 15: 1936–1746 BC with 95.4% probability) fit into the long time span for Bz A1 type objects between 2150 BC and 1700 BC.

The third burial, Rottenburg, Herderstraße, grave 1, contained a singular type of pin which does not appear in the Ruckdeschel system, but which Rüdiger Krause proposes to relate to Bz A2 shapes [25]. Due to the significant standard deviation, this old date (2137–1768 BC with 95.4% probability) does not contribute to a better understanding of the EBA chronology as it spans almost the complete EBA.

To conclude: the few radiocarbon dated burials with Bz A type objects are consistent with the late Bz A1 dates from Augsburg.

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