Attached to the castle, both in England and abroad, we frequently find an additional enclosure, much larger than the comparatively small area of the bailey proper. This was the _burgus_ or borough, which inevitably sprang up round every castle which had a lengthened existence. Our older antiquaries, finding that the word _burgenses_ was commonly used in Domesday in connection with a site where a castle existed, formed the mistaken idea that a _burgus_ necessarily implied a castle. But a _burgus_ was the same thing as a _burh_, that is, a _borough_ or fortified town. It may have existed long before the castle, or it may have been created after the castle was built. The latter case was very common, for the noble who built a castle would find it to his advantage to build a _burgus_ near it.[227] In exchange for the protection offered by the borough wall or bank, he could demand _gablum_ or rent from the burghers; he could compel them to grind their corn at his mill, and bake their bread at his oven; he could exact tolls on all commodities entering the borough; and if there was a market he would receive a certain percentage on all sales. The borough was therefore an important source of revenue to the baron. Domesday Book mentions the _new borough_ at Rhuddlan, evidently built as soon as the castle had been planted on the deserted banks of the Clwydd. In some cases a "new borough" is clearly a new suburb, doubtless having its own fortifications, built specially for the protection of the Norman settlers in England, as at Norwich and Nottingham.[228] That even in the 12th century a motte was considered an essential feature of a castle is shown by Neckham's treatise "De Utensilibus," where he gives directions as to how a castle should be built; the motte should be placed on a site well defended by nature; it should have a stockade of squared logs round the top; the keep on the motte should be furnished with turrets and battlements, and crates of stones for missiles should be always provided, as well as a perpetual spring of water, and secret passages and posterns, by which help might reach the besieged.[229]