On the other hand, we have undoubted evidence that the truncated conical form was common in post-Roman times. We have one, for instance, at Marlborough, close by, and if that place was Merlin's bury, as Sir R. Colt Hoare would fain persuade us it was, it assists us considerably in our argument. Without insisting on this, however, Mr. George Clark, in his most valuable paper on Ancient English Castles,[99] enumerates ninety truncated cones erected in England, he considers, between the Roman times and the Norman conquest. "These earthworks," he says, "may be thus described: First was cast up a truncated cone of earth, standing at its natural slope from 50 feet to 100 feet in diameter at the top, and from 20 feet to 50 feet high."[100] Mr. Clark does not believe that these were ever sepulchral, nor does it occur to him that they might be memorial. I should, however, be disinclined to accept the first conclusion as absolute till excavations had been made into some of them, at least, where I fancy we may find indications rather tending the other way. Whether they were memorial or not must depend on traditions that have not hitherto been looked for. Mr. Clark's contention was that all had at some time or other been used for residential purposes, and as fortifications, and many are recorded as having been erected as castles. All this is probably quite correct, but the point that interests us here is, that there are nearly one hundred examples of truncated cones of earth thrown up in England after the Roman times, and not one before. If this is so, the conclusion seems inevitable that Silbury Hill must belong to the latter age. Whether this conclusion can be sustained or not, must depend on what follows from the other monuments we are about to examine. The evidence of the monument itself, which is all we have hitherto had an opportunity of bringing forward, may be sufficient to render it probable, but not to prove the case. Unless other examples can be adduced whose evidence tends the same way, the case cannot be taken as proved, however strong a _prima facie_ presumption may be established. * * * * * [Illustration: 21. Marden Circle. From Sir R. C. Hoare. No Scale.]