Obsidian Distribution across Central Mexico

Information about obsidian consumption in Central Mexico comes from excavations at a limited number of sites (Table 1). During the Early Postclassic (AD 900–1200) at Xaltocan, most of the obsidian (68.9%) came from the Sierra de las Navajas source. The use of this green obsidian increased over time, climbing to 93.2% during the Late Postclassic (Millhauser Reference Millhauser and Brumfiel2005). This is not surprising, because Aztec influence facilitated the movement of Sierra de las Navajas obsidian throughout its territories. At Late Postclassic Chalco, obsidian from the Otumba and Sierra de las Navajas sources constitutes between 78% and 94% of the total obsidian assemblage (Elam et al. Reference Elam, Glascock, Neff and Hodge2008). The site of Cihuatecpan, in the Teotihuacan Valley, has the lowest proportion of Aztec-controlled sources of obsidian, but this can be attributed to the fact that only green obsidian is reported, with most of the gray obsidian likely originating from Otumba 3 km to the south (Figure 2). In general, sites in the Basin of Mexico relied heavily on Otumba and Sierra de las Navajas obsidian both before and during Aztec regional influence (Evans Reference Evans1988).

Table 1.

Distribution of Sierra de las Navajas and Otumba Obsidian Reported in Central Mexico Leading up to and during the Late Postclassic.

^aOp. 8 midden and surface materials not included.

^bContexts sorted through personal communication with David Carballo and Dave Walton.

^cData from personal communication with Patricia Plunket at the Universidad de las Americas, Puebla.

^dRecalculated by removing non-obsidian lithics from the total.

^eSamples come from multiple contexts, with long chronological ranges, thereby making it challenging to determine the time period. Most samples, however, come from the Classic period.

The consumption of green obsidian varies in the regions surrounding the Basin of Mexico (Table 1). During the Classic period, green obsidian from Sierra de las Navajas and gray obsidian from Ucareo, Michoacan, were the two major sources supplying sites in western Morelos. Ucareo became the dominant source provisioning Xochicalco during the Epiclassic (Hirth Reference Hirth2006; Hirth and Angulo Reference Hirth and Villaseñor1981). By the Middle Postclassic to Late Postclassic, the sites of Yautepec (Smith Reference Smith2006), Cuexcomate, and Capilco (Earle and Smith Reference Earle, Smith and Smith2012) steadily consumed green obsidian from Sierra de las Navajas, which constituted more than 90% of any assemblage.

Information on obsidian consumption is limited for the Tula area north of the Basin of Mexico except for the Epiclassic and Early Postclassic periods (Table 1). During the Epiclassic (Prado/Corral phases, AD 600–800), settlements primarily relied on the Ucareo-Zinapecuaro source located 150 km to the west. The distribution of green obsidian from Sierra de las Navajas (70 km to the east) at Tula and smaller sites, such as Cerro Magoni, was relatively low (<10%). By the Early Postclassic (Late Tollan phase, AD 1000–1100), exploitation of Sierra de las Navajas obsidian increased significantly in Tula (60%–85%) but only slightly in Cerro Magoni (18%; Anderson Reference Anderson, Faulseit, Xiuhtecuhtli and Mehta2018; Healan Reference Healan, Kowalski and Kristan-Graham2007, Reference Healan2012). This variation within the region points to complex exchange networks that greatly influenced access to obsidian sources.

In the Toluca Valley, the consumption of obsidian sourced from Sierra de las Navajas and Otumba increased steadily over time (Table 1). During the Classic and Epiclassic, the quantity of obsidian from these sources at Santa Cruz Atizapan was low, ranging between 13% and 15% (Benitez Reference Benitez2006). At Calixtlahuaca, the frequency of these two sources rose from 49.65% during the Middle Postclassic to 56.54% and, eventually, 70.46% by the end of the Late Postclassic (Huster Reference Huster2016). This steady growth of Sierra de las Navajas and Otumba obsidian points to the increase of trade between the Basin of Mexico and the Toluca Valley throughout the Postclassic.

What is important here is that the frequency of green obsidian from Sierra de las Navajas remained relatively steady in the Puebla-Tlaxcala region (Table 1). During the Classic period, information from Cholula and the site of Nealtican indicates that the southern Valley of Puebla was largely provisioned with green obsidian from Sierra de las Navajas, which constituted between 50% and 78% of lithic assemblages (Edelstein Reference Edelstein1995; Hirth Reference Hirth2013). In the northeastern part of the region at Cantona, green obsidian only made up 10% of the overall assemblage (Tellez Nieto Reference Tellez Nieto2013). This is a result, no doubt, of Cantona's location adjacent to the Zaragoza-Oyameles obsidian source that met most of its obsidian needs (Figure 2). The quantity of green obsidian arriving in central Puebla-Tlaxcala declined during the Epiclassic to between 12% and 19% at Xochitecatl-Cacaxtla and Cholula, when the former grew into a powerful regional center and the latter was partially abandoned (Edelstein Reference Edelstein1995; Hirth Reference Hirth2005; Plunket and Uruñuela Reference Plunket Nagoda and Ladrón de Guevara2018). During the Middle to Late Postclassic periods, the Puebla-Tlaxcala Valley was largely under the influence of the three altepemeh of Tlaxcala, Cholula, and Huexotzinco. Throughout the Postclassic, obsidian in the form of macrocores, polyhedral cores, and finished blades entered the region from a variety of sources. During the Late Postclassic it constituted only 5.6% of the obsidian assemblage at La Laguna, Tlaxcala, and 14%–16% of assemblages at Tepeticpac and other sites in the Tlaxcalan confederacy. At Cholula, green obsidian ranged from 18% to 23% for undifferentiated Postclassic deposits (Edelstein Reference Edelstein1995). Consequently, Sierra de las Navajas remained a relatively secondary resource of obsidian in the Puebla-Tlaxcala region.

Obsidian Consumption in Late Postclassic Tepeticpac, Tlaxcala

The altepetl of Tepeticpac is the oldest of the four central señorios within the Tlaxcalan confederacy (López et al Reference López Corral, Fargher and Cano2016). Tepeticpac was first occupied during the Epiclassic when it had a small residential population (López et al. Reference López Corral, Fargher and Cano2016; Muñoz Camargo Reference Muñoz Camargo and Chavero1892 [1576–1595]:53–54). As the first of the four señorios, Tepeticpac is located on a defensible hilltop (Figure 3) and was a major military center within the Tlaxcalan confederacy compared to the other three señorios of Tizatlan, Ocotelulco, and Quiahuiztlan (Aguilera Reference Aguilera1991:32; López and Santacruz Reference López Corral and Cano2010; Muñoz Camargo Reference Muñoz Camargo and Chavero1892 [1576–1595]:103). Tepeticpac's large public spaces, absence of luxurious elite palaces, and lack of iconography elevating a single individual or lineage have been used as evidence for communal or corporate leadership (Fargher et al. Reference Fargher, Blanton and Heredia Espinoza2010, Reference Fargher, Heredia Espinoza and Blanton2011, Reference Fargher, Blanton, Heredia Espinoza, Nichols and Rodríguez-Alegría2017; López et al. Reference López Corral, Fargher and Cano2016, Reference López Corral, Almanza, Ibarra Narváez and Cano2019). Tepeticpac was a large center that exerted considerable influence over the Puebla-Tlaxcala region. Its ceramic assemblage is different from that of neighboring Cholula and reflects a regional tradition shared by other sites within the Tlaxcalan domain. Tepeticpac's regional prominence made it an important center of obsidian consumption during the Late Postclassic (Millhauser et al. Reference Millhauser, Fargher, Heredia Espinoza and Blanton2015; Vicencio Reference Vicencio Castellanos2015; Xiuhtecutli Reference Xiuhtecutli, Faulseit, Xiuhtecuhtli and Mehta2018).

Archaeological excavations conducted in 2012 by Aurelio López and Ramón Santacruz Cano uncovered an elite residence, labeled CA-2 (Figure 3), near the summit of Tepeticpac (López and Santacruz Reference López Corral, Vera Ortiz, Cano, Hirth and Dyrdahl2015). The compound was a multiroom residence with partially intact stucco floors for three rooms connected by a hallway, one platform, and an external patio (Figure 4). The residence was occupied primarily during the Late Postclassic period as Tepeticpac rose to power; it continued to be occupied throughout the period of the supposed Aztec trade embargo and into the early colonial period. It was inhabited during Spanish contact, and its occupants would have been witnesses to and likely participants in the events of the conquest between AD 1519 and 1521.

Figure 4.

Map of Tepeticpac and location of CA-2 excavation (López et al. Reference López Corral, Vera Ortiz, Cano, Hirth and Dyrdahl2015:Figure 2).

Two mass spectrometer (AMS) radiocarbon (¹⁴C) assays from the Late Postclassic occupation were analyzed from this structure (Figure 5). The first sample dates to 435 ± 15 BP (PSUAMS-2715; charcoal). The 2σ calibrated age range is cal AD 1433–1464. The second sample dates to 330 ± 15 BP (PSUAMS-2717; seed) and has two possible 2σ calibrated age ranges; cal AD 1490–1603 (77.1%) and cal AD 1613–1637 (18.3%). Because the analyzed obsidian comes from a precontact level below the early colonial structure, we believe that the date falls within the former calibrated age range and very likely represents only prehispanic material (López et al. Reference López Corral, Gentil, Fargher, Alcantara and Cano2020).

Figure 5.

Late Postclassic / contact period excavation map from CA-2 (Vicencio Reference Vicencio Castellanos2015:Figure 8).

The obsidian from CA-2 consists primarily of finished pressure blades (73.1%). The obsidian debitage recovered from Late Postclassic levels indicates that a small amount of in-residence craft production was practiced at CA-2 consisting of obsidian biface and pressure blade production (Vicencio Reference Vicencio Castellanos2015:Table 19; Supplemental Table 1). Almost 16% of the obsidian assemblage consisted of green obsidian, which geochemical analysis has confirmed originated from Sierra de las Navajas (Supplemental Table 3). All the percentages discussed here and throughout this article are expressed in counts of artifacts.

Geochemical analysis was conducted on a random sample of 178 pieces of gray and black obsidian using pXRF to determine the other sources used to produce finished artifacts within the workshop. The results of these 178 determinations are presented in Supplemental Table 1 with the percentage of assemblage adjusted for the visual identification of Sierra de las Navajas pieces and summarizing all the obsidian sources represented in the collection. Obsidian from Paredón, Puebla, constitutes 59.2% of the collection. Three other gray obsidian sources are represented: Zaragoza-Oyameles, Puebla (12.8%); Otumba, Mexico (9.0%); and Pico de Orizaba, Puebla (3.3%; Vicencio Reference Vicencio Castellanos2015:Table 19). These findings appear comparable to those reported elsewhere in Tlaxcala. All four señorios—Tepeticpac, Ocotelulco, Quiahuiztlan, and Tizatlan—report percentages of obsidian from Sierra de las Navajas at about 14% by count and 12% by weight (Millhauser et al. Reference Millhauser, Fargher, Heredia Espinoza and Blanton2015; Xiuhtecutli Reference Xiuhtecutli, Faulseit, Xiuhtecuhtli and Mehta2018; see Table 1). Overall, Tepeticpac and its surrounding señorios obtained approximately 15% of their obsidian from the Aztec-controlled source of Sierra de las Navajas during the Late Postclassic period. When the Otumba source is included, the quantity of obsidian derived from Aztec-controlled sources rises to approximately one-quarter of all obsidian consumed at Tepeticpac. The ¹⁴C date of the CA-2 residence also makes it contemporaneous with the small rural obsidian workshop excavated at the Cinco Santos II site.

Obsidian Consumption and Production at Cinco Santos II

The site of Cinco Santos II (CSII) was located during the Proyecto Regional de Sitios Secundarios in Puebla-Tlaxcala (Gentil Reference Gentil2018). It falls within the Tlaxcalan confederacy and is located on a slope overlooking the valley corridor that connects the Puebla-Tlaxcala Valley with the Basin of Mexico (Figure 1). This corridor was an important communication route between Central Mexico and the Gulf coast (Carballo and Pluckhahn Reference Carballo and Pluckhahn2007; García Cook Reference García Cook, Sabloff and Andrews1981). If an embargo existed, this route would have been closely monitored to prevent the flow of goods into Tlaxcala.

CSII is a domestic site approximately 3 ha in size, located on a hillslope 14 km north of Tepeticpac and 1 km north of the Late Postclassic Tlaxcalan village site of Tlixpa. Obsidian production debitage was widespread, indicating that many of its households were involved in obsidian craft production. If raw materials were moving through commercial exchange networks, CSII's location along the natural transportation corridor into and out of the Basin of Mexico would have provided good access to obsidian from Otumba and Sierra de las Navajas, located 60 km and 95 km to the northwest, respectively. Conversely, we would expect these two sources to yield low percentages at CSII if the Aztec embargo were effective in restricting the flow of Basin of Mexico goods into Tlaxcala, especially because the source of Paredón is only 45 km north of the site.

Two areas were excavated at CSII, a domestic structure associated with an obsidian workshop and a small open platform that may have been a public assembly area. AMS radiocarbon dates were run on charcoal from sealed contexts in each area (Figure 5). This analysis established that CSII was a single-period occupation site that dated to the end of the Late Postclassic. The AMS ¹⁴C date from the domestic workshop was 480 ± 20 BP (PSUAMS-6413), which produced a 2σ calibrated age range of cal AD 1416–1446. The AMS ¹⁴C date from the open platform was 455 ± 20 BP (PSUAMS-6412) producing a 2σ calibrated age range of cal AD 1420–1455 (Figure 6). The calibrated ranges of both these dates place them prior to or shortly after the implementation of the proposed embargo.

Figure 6.

AMS calibrated dates. OxCal v4.3.2 Bronk Ramsey (Reference Bronk Ramsey2017); r5 IntCal13 atmospheric curve (Reimer et al. Reference Reimer, Bard, Bayliss, Warren Buck, Blackwell, Ramsey and Buck2013).

We recognize the difficulty of using radiocarbon methods to date archaeological remains to only a 60- to 70-year period. It should be noted that both CSII dates were from charcoal from posts, which raises the “old wood” issue for consideration; the trees used for the structure were cut 15–20 years before its final occupation (Dean Reference Dean1978; Schiffer Reference Schiffer1986). This implies that CSII closely aligns with the period of Aztec–Tlaxcala conflict. Ceramics recovered at CSII place the occupation of the site to the very end of the Late Postclassic period. Like CA-2, CSII also has a low percentage of early colonial ceramics in its assemblage, suggesting that it was occupied contemporaneously with Aztec–Tlaxcalan aggression and the proposed embargo. Given that obsidian was fundamental to the production of weaponry, we expect that it would have been a prime resource targeted by an economic embargo. Ethnohistorical sources indicate that Tenochtitlan seized control of towns near and leading to the Sierra de las Navajas source from Texcoco, which suggests it wanted to restrict access to the source, even by their allies (Pastrana and Carballo Reference Pastrana, Carballo, Nichols and Rodríguez-Alegría2017:Figure 22.1).

All the obsidian (1,978 pieces) collected from survey and excavations was analyzed using the lithic technology approach and assigned to the respective stage of production (Table 2). The primary production activity was the manufacture of obsidian prismatic blades. A total of 61.7% of the production debris was associated with blade manufacture, which included percussion core shaping (15.2%), pressure core shaping (15.9%), and final blade production (27.9%). The presence of corner blades and half-cylindrical core fragments in the assemblage indicates that craftspeople at CSII used both progressive and sequential core-reduction techniques to produce prismatic blades (Hirth et al. Reference Hirth, Severino, Johnson, Gentil, Cyphers, Hirth and Cyphers2020). General percussion flaking and some bifacial and unifacial production were also practiced (16.7%). Undiagnostic small flakes and flake shatter (21.7%) were recovered as well. The production activities identified reflect general-purpose production where obsidian blades were produced alongside expedient flakes and a few bifaces and unifaces.

Table 2.

Detailed CSII Obsidian Analysis of All Obsidian Organized by Technology and Differentiated between Green and Gray.

Table 2 separates green and gray obsidian into their respective technological categories. Technological analysis indicates that obsidian entered the workshop as both shaped macrocores and unworked nodules. The full range of core-shaping debitage using percussion and pressure techniques was recovered, indicating that macrocores had a small amount of cortex on one or more of their lateral surfaces. Unshaped nodules were used for both general percussion flaking and shaping a few bifaces and unifaces.

Source analysis was conducted as a two-step process. First, the amount of green obsidian, 11.8% of the CSII collection, was identified visually and confirmed as originating from Sierra de las Navajas with geochemical analysis (Supplemental Table 3). Second, geochemical analysis was then conducted on a sample of 148 gray obsidian artifacts using pXRF to determine the geological sources represented in the remaining gray obsidian sample. Four separate sources are represented in the gray obsidian: Paredón, Zaragoza, Otumba, and Pico de Orizaba. As can be seen in Table 3, Paredón is the dominant source. The obsidian from four of these sources, including Sierra de las Navajas, appears to have entered the workshop both as preformed macrocores for blade production and as small unworked nodules for bifacial general percussion reduction (Table 3). The same may also have been true of the Pico de Orizaba obsidian, although the sample is too small to determine whether this was the case.

Table 3.

CSII Obsidian Technological Analysis of 148 Obsidian Pieces Sourced via pXRF.

* See Table 2 for technological categories for Sierra de las Navajas.

The proportions of gray obsidian were then applied to the whole obsidian assemblage used in the CSII workshop during the Late Postclassic. These adjusted totals are presented in Table 3. Obsidian from Paredón constitutes 60.2% of the raw material reduced in workshop contexts, followed by obsidian from Zaragoza-Oyameles at 21.4%. The Valley of Mexico sources of Sierra de las Navajas (11.8%) and Otumba (4.8%) together represent 16.2% of the obsidian. Obsidian from the distant Pico de Orizaba occurs as trace amounts at 1.8% of the assemblage. The question that remains is this: What do the obsidian consumption and production data from Tepeticpac and CSII reflect about general economic patterns and the trade embargo believed to have been imposed on Tlaxcala by the Aztec state?