The Ouse, rising in the shires of Northampton and Bucks, and finally falling at King’s Lynn into the head of the Wash, flows deep and sluggish past Bedford, St. Neots, and Huntingdon, intersecting broad tracts of low and level land, now fertile meadow, but formerly almost impassable swamp, opposing great difficulties to the march of an invading force, especially if advancing from the eastern coast. At Eaton-Socon, between Bedford and Huntingdon, and a little above the town of St. Neots, the Ouse impinges upon the rising ground to the west, upon which stand Eaton Church and Village, and which afforded facilities for the construction of a large and lofty earthwork. This earthwork, known as the Castle Hill, is placed upon the west or left bank of the river, about 30 yards from its present brink, and a furlong or so from the fine parish church. It is possible that when the earthwork was first formed, the course of the stream lay at the foot of the banks. At present there is a large mill upon the river, a few yards above the castle, the leat of which is reunited to its parent stream opposite to the south-eastern edge of the fortress. The appended sketch shows the general plan of the place. It is, roughly speaking, a triangle, the east side, of 160 yards, resting upon the river, and the north side, of 140 yards, projecting from it at a right angle. The third side, or hypothenuse, is convex and irregular; measured upon the curve, it is in length about 220 yards. The area, complete, is about 3½ acres. The work is composed of three parts—an Inner, Northern, and Outer ward. The inner and north wards lie side by side upon the river, separated by a cross ditch. The two are contained within another ditch, which communicated at each end with the river. Beyond this, covering the south-western front, is the outer ward, and beyond this again the outer ditch, which commences at the south-east corner in the mill leat, covers the south-western front, and at the north-western angle sweeps round to join the ditch already mentioned, and thus, through it, to communicate with the river at the north-east corner of the work.