This article examines the construction of two military railways built on Romanian territory during the Russo–Ottoman War of 1877–1878: the Bender – Reni – Galați connecting line and the Frătești – Zimnicea branch, which linked the railway network to the Danube bridgehead at Zimnicea – Svištov. Drawing on contemporary documents, it reconstructs how these lines were planned and built under the pressures of wartime conditions. The article argues that the railways served as strategic instruments that compensated for the structural limitations of the prewar Romanian–Russian rail corridor. At the same time, the two case studies reveal the characteristic trade-offs of military railway construction: speed and carrying capacity were privileged over durability and economy. Particular attention is given to the frictions generated by customs exemptions, land acquisition and expropriation, administrative coordination between Romanian authorities and the Russian command, and the recruitment and management of labour, including the crisis surrounding the Italian workers employed on the Frătești – Zimnicea line.