Supporting Information

McConnell et al. 10.1073/pnas.1721818115

Fig. S1. Nearly contiguous annual average (black) and 11-y median-filtered (red) lead and related measurements in the NGRIP2 ice cores. Shown are 1100 BCE to 800 CE records of (A) total lead concentration, (B) enrichment relative to cerium, (C) estimated background lead concentration, and (D) nonbackground lead concentration and lead flux.

McConnell et al. www.pnas.org/cgi/content/short/1721818115 1of8 Fig. S2. Differences between ice-core chronologies. Differences between the new DRI_NGRIP2 ice-core chronology based on multiparameter, annual-layer counting and the independent IntCal13 age scale based on cosmogenic nuclides (1) at 137 volcanic tie points in both the GRIP and NGRIP2 ice-core records. Gray shading shows 1 σ uncertainties from mapping GRIP cosmogenic nuclides (10Be) on to IntCal13 (14C), suggesting <2-y uncertainties (1 σ) in the new chronology during . The DRI_NGRIP2 chronology differs from the NEEM_2011_S1 chronology (2) by <2 y throughout antiquity, well within the stated uncertainties of that chronology.

1. Adolphi F, Muscheler R (2016) Synchronizing the Greenland ice core and radiocarbon timescales over the Holocene–Bayesian wiggle-matching of cosmogenic radionuclide records. Clim Past 12:15–30. 2. Sigl M, et al. (2015) Timing and climate forcing of volcanic eruptions for the past 2,500 years. Nature 523:543–549.

Fig. S3. Differences between the original GRIP and DRI_NGRIP2 ice-core chronologies. The former, used to interpret the 18 previously published discrete measurements in the GRIP core of copper (1) and lead concentrations (2, 3), as well as lead isotope ratios (2), was incorrect by 20–30 y during classical antiquity.

1. Hong S, Candelone J, Patterson C, Boutron C (1996) History of ancient copper smelting pollution during Roman and medieval times recorded in Greenland ice. Science 272:246–249. 2. Rosman K, Chisholm W, Hong S, Candelone J, Boutron C (1997) Lead from Carthaginian and Roman Spanish mines isotopically identified in Greenland ice dated from 600 BC to 300 AD. Environ Sci Technol 31:3413–3416. 3. Hong S, Candelone JP, Patterson CC, Boutron CF (1994) Greenland ice evidence of hemispheric lead pollution two millennia ago by Greek and Roman civilizations. Science 265:1841– 1843.

McConnell et al. www.pnas.org/cgi/content/short/1721818115 2of8 Fig. S4. Lead deposition during antiquity measured in three European peat bogs and the NGRIP2 ice core (Fig. 1). Shown are the (A) Flanders Moss (Scotland) (1), (B) Myrarnar (Faroe Islands) (2), and (C) Penido Vello () (3) peat bogs with their chronologies adjusted within published dating uncertainties to match the NGRIP2 record. European peat bog records (black) are sensitive to both distal and proximal emissions. While overall trends match the NGRIP2 lead de- position record (red) during antiquity, the decline in flux during the Crisis of the documented in Greenland ice was not reflected in the peat bog records.

1. Cloy J, Farmer J, Graham M, MacKenzie A, Cook G (2008) Historical records of atmospheric Pb deposition in four Scottish ombrotrophic peat bogs: An isotopic comparison with other records from western Europe and Greenland. Global Biogeochem Cycles 22:GB2016. 2. Shotyk W, et al. (2005) Accumulation rates and predominant atmospheric sources of natural and anthropogenic Hg and Ph on the Faroe Islands. Geochim Cosmochim Acta 69:1–17. 3. Martinez Cortiza A, et al. (2002) Atmospheric Pb deposition in Spain during the last 4600 years recorded by two ombrotrophic peat bogs and implications for the use of peat as archive. Sci Total Environ 292:33–44.

McConnell et al. www.pnas.org/cgi/content/short/1721818115 3of8 a) Myrarnar b) Flanders Moss c) Penido Vello 2048 1097 588 315 169

91 /a)/(kg/s) 49 2 26 14 (ug/m 7 4 d) Myrarnar/NGRIP2 e) Flanders Moss/NGRIP2 f) Penido Vello/NGRIP2 128.00 32.00 8.00 2.00 0.50 0.13 0.03 0.01

Fig. S5. FLEXPART (1) emission sensitivity maps (A–C) at the three peat bog sites and ratios to the NGRIP2 emission sensitivity map (D–F). Locations of the three peat bogs (filled cyan circles) and the assumed center of Roman-era mining and smelting activities (unfilled red circle) are shown. Comparisonsofthe peat bog/NGRIP2 emission sensitivity ratio maps to the observed deposition ratios in the corresponding historical archives were used to identify locations of potential emissions assuming a common source. For example, the observed average deposition of pollution lead during the Roman Period was 0.45 and 60 μg/m2/a in the NGRIP2 ice and Flanders Moss peat bog cores, respectively. The ratio is on the order of 102. High ratios in emission sensitivities (E) are found in southwestern Europe and northern Africa, with ratios <10 for terrestrial sources located in North America, Asia, and eastern Europe that are inconsistent with the observed ratio in NGRIP2 ice and Flanders Moss peat.

1. Eckhardt S, et al. (2017) Source-receptor matrix calculation for deposited mass with the Lagrangian particle dispersion model FLEXPART v10.2 in backward mode. Geophys Model Dev 10:4605–4618.

McConnell et al. www.pnas.org/cgi/content/short/1721818115 4of8 Fig. S6. Sensitivity (1) of the NGRIP2 lead pollution record to atmospheric emissions estimated from FLEXPART atmospheric transport and deposition model simulations. Also shown are locations of known mining and ore processing sites during classical antiquity (2). Previous estimates of lead production based on historical and archaeological evidence (3) suggest that >60% of European lead production was from Iberia between 50 BCE and 500 CE and only ∼10% from Britain.

1. Eckhardt S, et al. (2017) Source-receptor matrix calculation for deposited mass with the Lagrangian particle dispersion model FLEXPART v10.2 in backward mode. Geophys Model Dev 10:4605–4618. 2. Wilson A, Friedman H (2010) Mining Database. Version 1.0. Available at oxrep.classics.ox.ac.uk/databases/mines_database/. Accessed May 21, 2017. 3. Nriagu JO (1983) Lead and Lead Poisoning in Antiquity (Wiley, New York).

McConnell et al. www.pnas.org/cgi/content/short/1721818115 5of8 Fig. S7. Annual average nonbackground lead deposition and estimated lead emissions with an 11-y median filter for 300 BCE to 300 CE (A) and 40 BCE to 300 CE (B). Gray shading indicates 22% uncertainty (1 σ) in emissions after filtering from year-to-year atmospheric transport variability. Also shown are the changing bullion content of Roman denarius coins (1), periods of major wars and plagues thought to have affected mining regions of southern Spain (Table S1), and selected historical events. Dashed line (blue) indicates when Roman pacification of Spain and was completed.

1. Butcher K, Ponting M (2015) The Metallurgy of Roman Silver Coinage: From the Reform of Nero to the Reform of Trajan (Cambridge Univ Press, Cambridge, UK).

McConnell et al. www.pnas.org/cgi/content/short/1721818115 6of8 Fig. S8. Assessment of underrecovery in NGRIP2. Measurement of total elemental concentrations may be influenced by acidification times since more re- calcitrant elements will remain in the particle phase longer than others and may not be fully recovered in the HR-ICP-MS analyses (e.g., refs. 1–3). To accurately assess underrecovery in the continuous NGRIP2 measurements, a subset of the acidified HR-ICP-MS sample stream (1% HNO3) was collected into precleaned 7-mL vials. The discrete vials were capped and stored. After storage for 4.5 mo, 32 vials were analyzed again. The average percentage increase in concentration relative to the appropriately averaged continuous measurements was 1% and 70% for lead (Pb) and cerium (Ce), respectively (A), indicating ∼100% recovery for lead and ∼60% recovery for cerium. The black circles in B show the corresponding ages for the 32 discrete samples. Also plotted are the continuous lead con- centration measurements (Fig. S1). Error bars in A are SEs.

1. McConnell JR, Aristarain AJ, Banta JR, Edwards PR, Simões JC (2007) 20th-century doubling in dust archived in an Antarctic Peninsula ice core parallels climate change and desertification in South America. Proc Natl Acad Sci USA 104:5743–5748. 2. Rhodes R, Baker J, Millet M, Bertler N (2011) Experimental investigation of the effects of mineral dust on the reproducibility and accuracy of ice core trace element analyses. Chem Geol 286:207–221. 3. Uglietti C, Gabrielli P, Olesik J, Lutton A, Thompson L (2014) Large variability of trace element mass fractions determined by ICP-SFMS in ice core samples from worldwide high altitude glaciers. Appl Geochem 47:109–121.

McConnell et al. www.pnas.org/cgi/content/short/1721818115 7of8 Table S1. Wars and campaigns affecting the and Civil Wars of the Roman Republic Name Start End Belligerent 1 Belligerent 2 Victor Theater of action

First Punic War −264 −241 Rome Carthaginian Mercenary −240 −238 Carthage Mercenaries Carthage North Africa (Tunisia) War −218 −201 Rome Carthage Rome Central and western Mediterranean Conquest of , −194 −179 Rome Spanish tribes Rome Spain including: Action in territory of −200 Central to southern War in 197 Two rebellions in the Guadalcuivir Warfare in Spain −196 −195 Warfare in Spain each −194 −191 year Warfare in Spain −188 Warfare in Spain −186 Warfare in Spain −184 Warfare in Spain −182 First Celtiberian War −181 −179 Rome Rome Celtiberia (Spain) Lusitanian War −155 −139 Rome Rome () Second Celtiberian War −154 −151 Rome Celtiberians Rome Celtiberia (Spain) −149 −146 Rome Carthage Rome North Africa (Tunisia) Numantine War −143 −133 Rome Numantians Rome Spain −124 −124 Rome Rome Southern Gaul −124 −121 Rome Arverni Rome Southern Gaul (Auvergne) −113 −101 Rome and Teutones Rome Southern Gaul, northern Italy −112 −106 Rome Numidians Rome North Africa (Tunisia, Algeria) Q. Servilius Caepio vs. −108 −107 Rome Lusitanians Rome Lusitania (Portugal) Lusitanians L. Caesius vs. Spanish tribe −104 −104 Rome Villaveijans Rome Villaveija near Alcantara Marius vs. Lusitanians −102 −102 Rome Lusitanians Rome Lusitania (Portugal) L. Cornelius Dolabella vs. −98 −98 Rome Lusitanians Rome Lusitania (Portugal) Lusitanians Titus Didius vs. Averaci −98 −98 Rome Averaci Rome Spain Titus Didius vs. Celtiberians −94 −94 Rome Celtiberians Rome Spain Crassus vs. Lusitanians −93 −93 Rome Lusitanians Rome Lusitania (Portugal) Social War −91 −88 Rome allies Rome Central Italy Flaccus vs. Celtiberians −88 −88 Rome Celtiberians Rome Spain First Sullan Civil War −88 −87 Marius Sullan faction Central Italy Second Sullan Civil War −83 −82 Sulla Marius the younger Sullan faction Central Italy Celtiberian rebellion −82 −82 Rome Celtiberians Rome Spain −80 −72 Sertorius + Metellus + Metellus + Pompey Southern and central Spain Caesar vs. Lusitanians −61 −61 Rome Lusitanians Rome Lusitania (Portugal) −58 −50 Rome Rome Gaul, Germania, Britannia Caesar’s Civil War −49 −45 Caesar Pompey Caesar Spain, Italy, Greece, Illyria, Egypt, Africa Post-Caesarian War −44 −43 Octavian Antony Octavian Italy Sicilian War −44 −36 Second Triumvirate Sextus Pompey Second Triumvirate Sicily Liberators’ War −43 −42 Second Triumvirate Brutus and Cassius Second Triumvirate Macedonia −41 −40 Octavian allies of Antony Octavian Rome, Perusia Final War of the Roman −32 −30 Octavian Antony and Cleopatra Octavian Greece and Egypt Republic Cantabrian and Asturian −29 −16 Rome Cantabrians and Rome Northwest Spain Wars Asturians

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Dataset S1 (XLSX)

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