By the middle of the eighteenth century this number had trebled. But even in 1801, as may be seen in Lyson's plan of the town, the King's Ditch, which was then still an open watercourse, remained substantially the boundary of inhabited Cambridge. And the vast suburban extensions in the areas of Barnwell, Newnham, Chesterton, and Cherry Hinton are mostly very recent indeed; the bulk in fact belonging to the last half century. Their rise, and the continuous intrusion of ever fresh University and College buildings, has had the effect of once more depleting the area of mediæval Cambridge, which to-day contains barely 800 houses. The whole of the University buildings, whether ancient or modern, are contained within this area, with the exception of the Colleges of Peterhouse, Pembroke, Christ's and Jesus (which together with a few of the Museums, stand just beyond the Ditch), and the New Court of St. John's College, which is on the other side of the river, in the old Common Field. The ecclesiastical and feminine foundations similarly situated, Selwyn College, Westminster College, Ridley Hall, Newnham College, and Girton College, are not recognised by the University as being strictly "Colleges" at all.