Physarum Itinerae: Evolution of Roman Roads with Slime Mould

Physarum Itinerae: Evolution of Roman Roads with Slime Mould

Emanuele Strano (Ecole Polytechnique Fédérale de Lausanne (EPFL), Switzerland and University of Strathclyde, Glasgow, UK), Andrew Adamatzky (University of the West of England, UK) and Jeff Jones (University of the West of England, UK)
Copyright: © 2011 |Pages: 25
DOI: 10.4018/jnmc.2011040103


The Roman Empire is renowned for sharp logical design and outstanding building quality of its road system. Many roads built by Romans are still used in continental Europe and UK. The Roman roads were built for military transportations with efficiency in mind, as straight as possible. Thus the roads make an ideal test-bed for developing experimental laboratory techniques for evaluating man-made transport systems using living creatures. The authors imitate development of road networks in Iron Age Italy using slime mould Physarum polycephalum. The authors represent ten Roman cities with oat flakes, inoculate the slime mould in Roma, wait as mould spans all flakes-cities with its network of protoplasmic tubes, and analyse structures of the protoplasmic networks. The authors found that most Roman roads, a part of those linking Placentia to Bononia and Genua to Florenzia are represented in development of Physarum polycephalum. Transport networks developed by Romans and by slime mould show similarities of planar proximity graphs, and particular minimum spanning tree. Based on laboratory experiments the authors reconstructed a speculative sequence of road development in Iron Age Italy.
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1. Introduction

Developing physical, chemical and biological analogies of socio-economic processes are becoming increasingly popular nowadays because they give rise to new metaphors and uncover unique similarities. Successful examples of such cross-disciplinary fertilisation include the theory of fractal cities (Batty & Longley, 1994), leaf-inspired simulation of street network growth (Runions, Fuhrer, Lane, Federl, Rolland-Lagan, & Prusinkiewicz, 2005; Barthelemy & Flammini, 2008), urban theories by Alexander (1964) and Salingaros (2005), approaches relating urban morphology to biological morphogenesis (Mouson, 1997), and indeed the whole branch of socio-physics (Galam, 2012).

Despite the overwhelming success of the bio-inspired simulation and socio-physics, the prevailing majority of publications deal with purely theoretical works and computer simulations. Almost no attempts have been made to undertake experimental laboratory comparisons between very large-scale socio-economic developments and spatio-temporal dynamics of chemical or biological systems. This could be explained by difficulties in finding a suitable experimental substrate which does not require sophisticated laboratory equipment and expensive support. A breakthrough came in 2009 when first experimental results on imitating roads networks in United Kingdom with plasmodium of slime mould Physarum polycephalum were published (Adamatzky & Jones, 2010) followed by imitation of rail networks in Japan (Tero et al., 2010).

Plasmodium is a vegetative stage of acellular slime mould Physarum polycephalum. This is a single cell with many nuclei. The plasmodium fees on microscopic particles (Stephenson & Stempen, 2000). During its foraging behaviour the plasmodium spans scattered sources of nutrients with a network of protoplasmic tubes. The protoplasmic network is optimised to cover all sources of food and to provide a robust and speedy transportation of nutrients and metabolites in the plasmodium body. The plasmodium’s foraging behaviour can be interpreted as computation. Data are represented by spatial configurations of attractants and repellents, and results of computation by structures of protoplasmic network formed by the plasmodium on the data sites (Nakagaki, Yamada, & Ueda, 2000; Nakagaki, Yamada, & Toth, 2001; Adamatzky, 2010a). The problems solved by plasmodium of P. polycephalum include shortest path (Nakagaki, Yamada, & Ueda, 2000; Nakagaki, Yamada, & Toth, 2001), implementation of storage modification machines (Adamatzky, 2010a), Voronoi diagram (Shirakawa, Adamatzky, Gunji, & Miyake, 2009), Delaunay triangulation (Adamatzky, 2010a) logical computing (Tsuda, Aono, & Gunji, 2004; Adamatzky, 2010b), and process algebra (Schumann & Adamatzky, 2009; see overview in Adamatzky (2010a).

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