This article describes identified sections of an early 18th century ditch at Fort Umrevinsky in the Upper Ob Basin. Such protective structures mark a certain stage in the evolution of military engineering in the era of Peter the Great (1694–1725) in southwestern Siberia. The design of the earliest parts of the preserved ditches allows us to address the influence of European fortification on Early Modern Russian defensive architecture. Several factors affecting the depth and profile of early 18th century ditches at Umrevinsky are discussed. They include seasonality of specialized trenching tools and the adoption and transformation of European fortification principles by 17th and early 18th Russian military engineers. At Umrevinsky, apart from the specific profile of the ditch, specialized tools were revealed, similar to those mentioned in documents on 18th century fortification. Also, specific features of the preserved parts of the ditch mirror the utmost irregularity in adoption of de Vauban’s fortification principles of the Tsardom of Muscovy, including Siberia. Our finds at Fort Umrevinsky supplement the scarce descriptions of Siberian forts in Russian documents.