The study describes the findings of excavations at the northern palisade of Fort Umrevinsky. We revealed the basis of a log structure with a floor made of planks, adjoining the central part of the northern palisade. A tight joining of the palisade ditch with the two preserved rows of logs indicates a single construction episode. At this area, another entrance to the territory of the fort was revealed, situated right opposite the southern one. Design features of the foundation of the log structure (the way of cutting logs, the floor made of planks), dimensions (6 × 6 m), and location suggest that this was the base of the northern passage tower. Spatial structure, location, and size of the structure match those of wooden towers of Siberian forts. During earlier studies at one of the corner towers of Fort Umrevinsky, built as early as the second quarter of the 18th century, a plank floor was also revealed. The northern passage tower was erected at the initial stage (before the first third of the 18th century) of the fort’s existence. This wooden defensive structure suggests that Fort Umrevinsky was one of border fortifications, each of which had a sub-rectangular palisade and a single entrance tower. The foundation of the northern entrance tower was probably described in 1741 by J.G. Gmelin as a ruin of a guardhouse. Towers of Siberian forts were multifunctional. Apart from their defensive function, they served as guardhouses and were also destined for living and storage.