The Archaeology and History of Bitumen

Bitumen—also known as asphaltum or tar—is a black, oily, viscous form of petroleum, a naturally-occurring organic byproduct of decomposed plants. It is waterproof and flammable, and this remarkable natural substance has been used by humans for a wide variety of tasks and tools for at least the past 40,000 years. There are a number of processed types of bitumen used in the modern world, designed for paving streets and roofing houses, as well as additives to diesel or other gas oils. The pronunciation of bitumen is "BICH-eh-men" in British English and "by-TOO-men" in North America.

What Bitumen Is

Natural bitumen is the thickest form of petroleum there is, made up of 83% carbon, 10% hydrogen and lesser amounts of oxygen, nitrogen, sulfur, and other elements. It is a natural polymer of low molecular weight with a remarkable ability to change with temperature variations: at lower temperatures, it is rigid and brittle, at room temperature it is flexible, at higher temperatures bitumen flows.

Bitumen deposits occur naturally throughout the world--the best known are Trinidad's Pitch Lake and the La Brea Tar Pit in California, but significant deposits are found in the Dead Sea, Venezuela, Switzerland, and northeastern Alberta, Canada. The chemical composition and consistency of these deposits vary significantly. In some places, bitumen extrudes naturally from terrestrial sources, in others it appears in liquid pools which can harden into mounds, and in still others it oozes from underwater seeps, washing up as tarballs along sandy beaches and rocky shorelines.

Uses and Processing

In ancient times, bitumen was used for a huge number of things: as a sealant or adhesive, as building mortar, as incense, and as decorative pigment and texture on pots, buildings or human skin. The material was also useful in

waterproofing canoes and other water transport, and in the mummification process toward the end of the New Kingdom of ancient Egypt.

The method of processing bitumen was nearly universal: heat it until the gasses condense and it melts, then add tempering materials to tweak the recipe to the proper consistency. Adding minerals such as ochre makes bitumen thicker; grasses and other vegetable matter add stability; waxy/oily elements such as pine resin or beeswax make it more viscous. Processed bitumen was more expensive as a trade item than unprocessed, because of the cost of the fuel consumption.

The earliest known use of bitumen was by Middle Paleolithic Neanderthals some 40,000 years ago. At Neanderthal sites such as Gura Cheii Cave (Romania) and Hummal and Umm El Tlel in Syria, bitumen was found adhering to stone tools, probably to fasten a wooden or ivory haft to the sharp-edged tools.

In Mesopotamia, during the late Uruk and Chalcolithic periods at sites such as Hacinebi Tepe in Syria, bitumen was used for the construction of buildings and water-proofing of reed boats, with among other uses.

Evidence of Uruk Expansionist Trade

Research into bitumen sources has illuminated the history of the expansionist period of Mesopotamian Uruk. An intercontinental trading system was established by Mesopotamia during the Uruk period (3600-3100 BC), with the creation of trading colonies in what is today southeastern Turkey, Syria, and Iran. According to seals and other evidence, the trade network involved textiles from southern Mesopotamia and copper, stone, and timber from Anatolia, but the presence of sourced bitumen has enabled scholars to map out the trade. For example, much of the bitumen in Bronze age Syrian sites has been found to have originated from the Hit seepage on the Euphrates River in southern Iraq.

Using historical references and geological survey, scholars have identified several sources of bitumen in Mesopotamia and the Near East. By performing analyses using a number of different spectroscopy, spectrometry, and elemental analytical techniques, these scholars have defined the chemical signatures for many of the seeps and deposits. Chemical analysis of archaeological samples has been somewhat successful in identifying the provenance of the artifacts.

Bitumen and Reed Boats

Schwartz and colleagues (2016) suggest that the onset of bitumen as a trade good began first because it was used as waterproofing on the reed boats that were used to ferry people and goods across the Euphrates. By the Ubaid period of the early 4th millennium BC, bitumen from northern Mesopotamian sources reached the Persian Gulf.

The earliest reed boat discovered to date was coated with bitumen, at the site of H3 at As-Sabiyah in Kuwait, dated about 5000 BC; its bitumen was found to have come from the Ubaid site of Mesopotamia. Asphaltum samples from the slightly later site of Dosariyah in Saudi Arabia, were from bitumen seepages in Iraq, part of the wider Mesopotamian trade networks of Ubaid Period 3.

The Bronze Age Mummies of Egypt

The use of bitumen in embalming techniques on Egyptian mummies was important beginning at the end of the New Kingdom (after 1100 BC)--in fact, the word from which mummy is derived ' mumiyyah' means bitumen in Arabic. Bitumen was a major constituent for Third Intermediate period and Roman period Egyptian embalming techniques, in addition to traditional blends of pine resins, animal fats, and beeswax.

Several Roman writers such as Diodorus Siculus (first century BC) and Pliny (first century AD) mention bitumen as being sold to Egyptians for embalming processes. Until advanced chemical analysis was available, black balms used throughout the Egyptian dynasties were assumed to have been treated with bitumen, mixed with fat/oil, beeswax, and resin. However, in a recent study Clark and colleagues (2016) found that none of the balms on mummies created prior to the New Kingdom contained bitumen, but the custom began in the Third Intermediate (ca 1064-525 BC) and Late (ca 525-332 BC) periods and became most prevalent after 332, during the Ptolemaic and Roman periods.

Bitumen trade in Mesopotamia continued well after the end of the Bronze Age. Russian archaeologists recently discovered a Greek amphora full of bitumen on the Taman peninsula on the northern shore of the Black Sea. Several samples including numerous large jars and other objects were recovered from the Roman-era port of Dibba in the United Arab Emirates, containing or treated with bitumen from the Hit seepage in Iraq or other unidentified Iranian sources.

Mesoamerica and Sutton Hoo

Recent studies in pre-Classic and post-classic period Mesoamerica have found bitumen was used to stain human remains, perhaps as a ritual pigment. But more likely, say researchers Argáez and associates, the staining may have resulted from using eated bitumen applied to stone tools which were used to dismember those bodies.

Fragments of shiny black lumps of bitumen were found scattered throughout the 7th-century ship burial at Sutton Hoo, England, in particular within the burial deposits near remains of a helmet. When excavated and first analyzed in 1939, the pieces were interpreted as "Stockholm tar", a substance creating by burning pine wood, but recent reanalysis (Burger and colleagues 2016) has identified the shards as bitumen having come from a Dead Sea source: very rare but clear evidence of a continuing trade network between Europe and the Mediterranean during the early Medieval period.

Chumash of California

In California's Channel Islands, the prehistoric period Chumash used bitumen as body paint during curing, mourning and burial ceremonies. They also used it to attach shell beads onto objects such as mortars and pestles and steatite pipes, and they used it for hafting projectile points to shafts and fishhooks to cordage.

Asphaltum was also used for waterproofing basketry and caulking sea-going canoes. The earliest identified bitumen in the Channel Islands so far is in deposits dated between 10,000-7,000 cal BP at Cave of the Chimneys on San Miguel island. The presence of bitumen increases during the Middle Holocene (7000-3500 cal BP and basketry impressions and clusters of tarred pebbles show up as early as 5,000 years ago. The fluorescence of bitumen may be associated with the invention of the plank canoe (tomol) in the late Holocene (3500-200 cal BP).

Native Californians traded asphaltum in liquid form and hand-shaped pads wrapped in grass and rabbit skin to keep it from sticking together. Terrestrial seeps were believed to produce a better quality adhesive and caulking for the tomol canoe, while tarballs were considered inferior.