Plant economy in the westernmost territory of the Roman state through waste: the wet site of O Areal (Vigo, Spain)

: The Roman economy of the Iberian Peninsula has habitually been characterised in terms of prestige goods and economic activities such as trade, mining and metallurgy. The analysis of plant-based foods –less prestigious but more essential in everyday life– has commonly been marginalised in state-of-the-art reviews. The O Areal saltworks is exceptional in terms of the large number of organic materials it preserves, and the excellent state of that preservation. After its abandonment (end of the 3rd/4th century AD), the saltworks was briefly used as a dumping ground for the surrounding area. The site's archaeobotanical remains, preserved under anoxic, waterlogged conditions, consist of the building materials used at the saltworks, tools and other artefacts, organic objects employed in activities such as fishing, and refuse. The assemblage suggests a wide diversity of species to have been introduced into northwestern Iberia during the Roman Period, including the mulberry, peach, fig, plum, grapevine, and melon. The notable presence of other edible fruit species that normally grew wild during this period, such as chestnut, walnut, stone pine, and cherry trees, might be related to the start of their cultivation.


Introduction
The representativeness of plants in the archaeobotanical record is conditioned by many factors, including their selection and transformation by humans, the environmental and edaphic conditions where the remains were deposited, their alteration by biotic factors, the stability of the deposition conditions, and how such materials were recovered and stored during archaeological excavations. Plant materials for which fire is involved at some point in their gathering, processing, storage, consumption or discarding, are commonly much better represented than those that are consumed fresh, require much processing, or that rapidly perish.
Although the Iberian Peninsula has a diversity of climatic conditions, the seeds and fruits Constantly submerged, waterlogged sediments facilitate the preservation of organic matter, including that used to make objects. The oxygen turnover is slow, generating conditions unsuitable for microbial growth, consequently reducing the rate of degradation (Bleicher and Schubert 2015). This allows for the better preservation of leaves, pericarps, endocarps, woody materials and fibres commonly broken down at dry sites, although it does not favour the preservation of cereal caryopses (their recovery from wet sites is unusual). The organic remains found at wet sites can, of course, have been affected by transport or re-deposition (Antolín et al. 2017a), or changes in the physicochemical conditions and relative humidity of the surrounding water and sediment (Martín Seijo et al. 2010).   Tereso et al. 2020;Vaz et al. 2016).
It is not easy to trace the biographies of many of these new crops in the archaeobotanical literature. The arrival of Mediterranean peoples could have driven the development of innovative agricultural practices and led to the domestication of certain local species, new domestic varieties, and perhaps even allowed for genetic exchange with wild varieties, as suggested for grapevine (Cunha et al. 2020;Freitas et al. 2021;Riaz et al. 2018). The same may have been true for other species at this time, such as chestnut (Castanea sativa), apples/pears (Pyrus/Malus), olive (Olea europaea) or sweet cherry (Prunus avium); species that frequently appear in archaeobotanical assemblages (cf. Peña-Chocarro et al. 2019) but whose remains offer little information regarding a wild or domestic origin. The context in which they are found, and their frequency, need to be taken into account in any interpretation of their presence. Some crops, e.g., citrus fruits (Citrus medica and Citrus limon -the citron and lemon respectively) known from texts, pictorial representations and preserved seeds and fruits (Zech-Matterne and Fiorentino 2017) to have been present in other parts of the Roman State, e.g., the Italian Peninsula, did not arrive in the Iberian Peninsula in Roman Period according to current data (Peña-Chocarro et al. 2019). The same is true for black pepper (Piper nigrum), bottle gourd (Lagenaria siceraria), sesame (Sesamun indicum), and rice (Oryza sativa) (Bakels and Jacomet 2003;Bosi et al. 2020;Jacomet and Vandorpe 2011;Livarda 2011;Wiethold 2003).
Their absence (and that of other species) may be due, however, to a) the need for further archaeobotanical study, b) these species being associated -in very specific contexts-with poorer social classes or high-status individuals, or c) differences in the adoption of the same species within the different territories that made up the state. Knowing the reasons why crops were accepted or not in each territory allows for the economic transformations that took place, and the preferences and habits in food and drink, to be observed, bringing us closer to understanding how society changed, and to comprehending the intercultural context that laid the foundations of Roman culture in Iberia.

Objectives
The O Areal saltworks provides an opportunity to gain new knowledge about the use of plant species by human communities during the Roman Period in the Iberian Peninsula,

Materials and methods
The archaeobotanical samples examined in this work come from the Unidade de Actuación I-06 in Rosalía de Castro Street, Vigo (Spain), an archaeological area that was excavated over five archaeological campaigns between 2006 and 2008. Their geographical location refers to the outline of the stratigraphic units of origin; xyz coordinates were not provided. The sediment comes from the deposit of organic matter that appeared after the abandonment of the saltworks, and from successive levels of fill that formed over the saltworks' ponds. Of the total 127 samples collected, 115 were analysed. Most were manually collected and included worked wooden objects and the remains of seeds and fruits; 29 samples were either wet or dry sediment that required processing to extract their contents (see below).
The majority of the examined remains were collected during the CD 102A 2006/368 campaign in sediment from stratigraphic unit SU1049, a wet and sandy-loamy deposit formed inside the evaporation ponds. This was covered by a sand dune up to 1 m in height with several levels of organic matter interspersed in its lower part. It preserved huge quantities of organic matter such as plant macrofossils -wood, fruits, seeds, leaves-, leather, fish scales and other ichthyological remains. Each sediment sample from SU1049 was sub-sampled (volume 3 L) and the contents analysed; the subsampling of small volumes of sediment has been shown sufficient for constructing representative records of wet sites for the study of their associated economy (Antolín et al. 2017b).
The dry sediment samples collected were processed using a flotation machine to recover the remains. The wet sediment samples, in contrast, were sieved to the wash-over technique in a bucket -no pressurised water was used- (Steiner et al. 2015). The floating material recovered using both techniques was poured onto sieves of 2, 1 and 0.5-mm mesh size for separation.
Some of the organic material was subjected to desalination and the elimination of oil by means of a solution of water and neutral soap. This oil comes from spillages from a 20th century canning factory built over part of the archaeological area. The remains were stored immersed in still water inside rigid packaging and kept in a cold chamber to prevent the proliferation of microorganisms. Table 1 provides information on the sampling and processing performed. The remains were then sorted according to their state of preservation using a trinocular microscope at 1-7x magnification. For material from the sediment, this was performed dry; for the waterlogged material it was sorted in a sheet of water to avoid moisture loss which would accelerate the rate of physical alteration or chemical degradation. The anatomical characteristics of seeds and fruits were compared against the reference collection of the

Results
The total of 2716 carpological remains (individual seeds, seed fragments, and other plant parts) were recovered. Most were waterlogged; only five charred cereals remains were found. The concentration of carpological remains in the sediment samples from inside the evaporation ponds (SU1049) and processed by the wash-over technique was 1320/L, much greater than that obtained by flotation from samples taken outside of SU1049 (0.09/L). A total of 37 species and 13 genera within 28 families were identified; some could not be identified. These are high counts given the relatively small number of samples processed, and include plants cultivated and/or managed by humans, plus species that grew naturally but whose presence was influenced by the artificial environment produced by the saltworks. Table 2 summarises the species found and their abundance. Panicum miliaceum (lemma/palea) 1508 9 Triticum aestivum/durum (seed) 4 Orchard/Garden Apium graveolens (mericarp) 2 3 Cucumis melo (seed) 3 Cucumis melo/sativus (seed fragment) 1 Physalis alkekengi ( Medicago polymorpha (fruit) 1

Cereals
Cereals were the best represented of all plant types in terms of abundance. Most remains corresponded to paleas and lemmas of broomcorn millet (Panicum miliaceum); indeed, this species accounted for 55.85% of the remains of the entire assemblage. Four caryopses of wheat (Triticum aestivum/durum) and one rachis of barley (Hordeum vulgare) were also documented.
These species of the tribe Triticeae accounted for all five charred remains recovered.

Horticultural and garden species
Melon seeds (Cucumis melo) were recovered in small numbers. Remains of celery (Apium graveolens) and bladder cherry (Physalis alkekengi) were also found in small numbers.
Notwithstanding the fact that celery and bladder cherry can be understood as wild plants, here it is proposed both species were cultivated (see Discussion).

Fruit trees
Fruit-tree and fruit-shrub species were well represented in the samples.

Weeds and ruderal species
Many species of weed were identified, the growth of which may have been favoured by the niches created by agricultural exploitation (some are frequently present in communities associated with cereal fields). These included Chenopodium album, Glebionis segetum, Medicago polymorpha, Portulaca oleracea, Polygonum aviculare, Polygonum lapathifolium, Polygonum persicaria. Other species common in anthropised environments, such as Atriplex prostrata, Silene dioica, Silene vulgaris and Urtica dicoica, were also found.

Wild plants
Some of the documented remains belonged to fruit-bearing species, though no evidence of consumption was detected. These included an immature acorn of Quercus sp. and complete individuals (hazelnuts) of Corylus avellana, some with rodent bites, making it feasible that their presence is the result of transport or that they were simply natural inclusions. Elder (Sambucus nigra) and alder buckthorn (Frangula alnus) seeds and other remnants were also found. These plants grow naturally in humid environments in the northwestern Iberian Peninsula and produce fruits that may have provided human food. The presence of blackberry (Rubus fruticosus) seeds and spines indicates the existence of this plant in the surrounding area.
Reeds (Arundo/Phragmites), compact rush (Juncus conglomeratus/effusus) and watercress (Nasturtium officinale) also found suitable places to grow; they may have formed part of the natural background or may have proliferated at the site.

Discussion
The O Areal site contains a unique array of species that helps us understand the changes in the agricultural economy that occurred in the Iberian Peninsula during Roman times. However, care should be exercised when drawing conclusions. The primary context of the plants used for food is unknown, as are the areas where they were cultivated and the background against which they were processed. The examined remains were all found in a waste dump with anthropogenic and natural inputs, and although they are exceptionally well preserved, sampling was undertaken during excavation campaigns, making the results impossible compare with those obtained by systematic archaeobotanical sampling at other wet sites (cf. Antolín et al. 2017b; Maier and Harwath 2011, among others).

Plants in the surroundings of O Areal
The results indicate that different components of cereal processing were undertaken in the area around the saltworks. Although cereal caryopses are poorly preserved in damp environments, the woody parts of broomcorn millet were well preserved, providing the largest quantity of remains analysed for this species. These remains are likely a by-product of winnowing or the digested remains of animal feed. Two ways of dehusking the grain from the covers have been recorded for millet, namely pounding and grinding, which leaves the paleas and lemmas It is difficult to establish whether other common and ruderal plants detected at O Areal were present in the natural environment or linked to gardens and horticultural land, as some of them were used in Roman times but this cannot be deduced from the samples analysed at the site.
For example, bladder cherry is not naturally occurring in the northwestern Iberia (vid. Romero Buján 2008), but it was present in the wild in other areas of the Iberian Peninsula during prehistoric times (Antolín 2016). Its fruit has a diuretic effect and cures jaundice according to Dioscorides; therefore, bladder cherry may have been introduced into the settlement for medicinal or even ornamental purposes. Henbane is a good proxy for soil fertility due to their prevalence in rich soils (Grime et al. 1988) but it has also psychotropic properties highly appreciated by the Greek physician Dioscorides (De materia medica 4.68.1) in the 1st century A.D. (Scarborough 2018). Their seeds were used as a local anaesthetic and were prepared in an ointment with wool fat for treating soldiers' pain (Belfiglio 2017). Henbane has also been recorded at other sites in northwestern Iberia (Tereso et al. 2020;Vaz et al. 2017), although it has not been associated with any medicinal use and here is considered as a weed.
Perhaps the most important aspect of this archaeobotanical assemblage is the variety of consumable fruits identified. Chestnut, walnut, cherry and stone pine have been grown in tree formations since ancient times (Carrión 2012), but they also grow wild, so it is hard to say whether wild or cultivated varieties  -Seijo et al. 2020;Silva 2008). All these species were potentially used for food, but no evidence is available of their use or transport to sites in northwestern Iberia or the Cantabrian area (northern Iberia) during the Iron Age. However, given the biography of these fruit trees and the frequency with which they began to appear in Roman settlements, the expansion of their cultivation and consumption probably began in Roman times.
The remains of fruits of Castanea sativa and Juglans regia were recovered in a highly fragmented state, perhaps indicating intentional fragmentation for consumption. It is also possible that part of the fruits was deposited as a natural inclusion due to the existence of specimens close to the saltworks; these may have then suffered degradation for different reasons (see Antolín et al. 2017a). However, the type of fragmentation seen for the bracts of were not available for the present study.
The remains of adventitious and ruderal species were present. These taxa are compatible with a profoundly transformed environment, and are frequently found in hedges, along roads, and in fields, etc. Corylus avellana, Rubus fruticosus and Sambucus nigra were also detectedamong other species-but no evidence of their use or consumption was found.

Roman towns as centres for the introduction of crops
The O Areal site presents an assemblage of species with numerous parallels across Europe The Roman Period witnessed a transformation in the productive landscape in terms of tree species. The cultivation of fruit trees required changes in spatial organisation, and a workforce dedicated to orchard maintenance and the distribution of the fruit to markets. Urban centres even generated new habitats mediated by humans, including the formation of gardens, and leisure spaces, and in these plants may have been cultivated for their beauty or medicinal properties. A conception of plants beyond their use as food or as part of a productive activity is provided by species grown for ornamental reasons, e.g., the cypress trees (Cupressus sempervirens) at the thermal baths of Aquae Flaviae (Vaz et al. 2016). Juglans regia and Pinus pinea/pinaster were also planted for funerary rites; the quality of their wood for crematory fires and their significance in Roman culture (Martín-Seijo and César Vila 2019) would have made them good choices.

Conclusions
The state of preservation of the waterlogged materials at O Areal allowed the identification of species not commonly found at sites in the Iberian Peninsula, where the macroremains of fruits and seeds are usually preserved either in carbonised or mineralised form. They also allow the biography and consumption of plants to be traced during the Roman Period in the northwest of the Iberian Peninsula and reflect the transformations in agricultural practices that were underway such as arboriculture. The tree and shrub species detected, i.e., Castanea sativa, Other species, such as the cereals Panicum miliaceum, Triticum aestivum/durum, Hordeum vulgare, and horticultural species such as Cucumis melo and, probably, Apium graveolens and Physalis alkekengi, were also detected, as were several species belonging to weed communities linked to cropland. The results also provide data on the surrounding plant communities.
Although the influence of a productive and strongly altered area for making salt influenced the composition of the archaeobotanical assemblage, some of the taxa identified would have grown