The next lock is Clayhithe, two miles further down the river, with an inn beside it in special favour for Cambridge boating pic-nics. Here, too, is the lowest bridge over the Cam, indeed the only one below Cambridge. It belongs to a private company, and is rigorously tolled. A pretty shady lane leads to it from Horningsea. Hard by, on the left bank, are the villages of Waterbeach and Landbeach. They are respectively four and twelve furlongs from the stream, and mark successive boundaries of the fenland waters. Between them runs an ancient earthwork, the Car Dyke (probably of Roman date), which of old kept those waters in flood time from drowning the meadows to the south. Starting from the Cam at Clayhithe it runs along the whole western limit of the fenland. It reaches the Ouse near the large village of Cottenham (where the east window of the fourteenth century church is copied from one in Prior Crauden's Chapel at Ely) with over 2,000 inhabitants, and goes on past the tiny and picturesque Rampton, with under 200, to Willingham and Earith, Ramsey and Peterborough, Deeping and Sleaford; finally ending its long course on the banks of the far off Witham, hard by Lincoln. [Illustration: _Swavesey Church._] For a mile or so our "Akeman Street" follows the course of the Car Dyke, and then strikes northward across the fen, along a causeway of its own, passing near the remains of Denny Abbey, a small foundation which passed through unusual vicissitudes. Originally a Benedictine House, it was transferred in the twelfth century to the Templars, and in 1290, passed from them to the Minor Sisters of the Franciscan order. Marie de Valence, the foundress of Pembroke College, was a noted benefactress to Denny, and in her statutes solemnly enjoined on the scholars of the former institution "kindness" towards the recluses of the latter. The abbey is now a farm, but there are more remains of the monastic buildings here than almost anywhere else in the county. Much of the church is built into the farm house, and the refectory is in use as a barn. Many old walls and dykes may be traced, while a large entrenchment to the south is known as "Soldiers' Hill." This name may be due to the Templars.