From Barter to Blockchain: The Evolution of Price in the Law of Sale

This chapter examines the legal concept of price in the contract of sale (emptio venditio) from its Roman origins to the contemporary debate on cryptocurrencies. The study aims to identify the essential legal func- tion of price – as a stable and publicly recognised measure of value – and to assess whether emerging digital assets are capable of fulfilling that function. The central hypothesis, grounded in Paul’s analysis in Dig. 18.1.1, is that money performs the role of price not by virtue of its material substance but through its character as a conventional param- eter endowed with aestimatio publica ac perpetua. The analysis em- ploys a legal-historical method, tracing the evolution of Roman coinage from aes rude through the gold standard to modern fiat money, and then applies the resulting framework to cryptocurrencies, drawing on EU and national case law (CJEU Case C-264/14, Italian Court of Cas- sation judgment No. 1760/2025, Spanish Tribunal Supremo judgment No. 326/2019). The findings show that cryptocurrencies, despite their capacity to transfer value, lack the stability and institutional recogni- tion required to function as a legal price; a transaction settled in cryp- tocurrency must accordingly be classified as barter rather than sale, a conclusion already implicit in the Roman juristic tradition.