o the
greater solidity of the former; the shell keeps were far more numerous
in the twelfth century; and the reasons for this are obvious--the
rectangular keep was much more expensive to build, and it was too
heavy to erect on the artificial mounds on which the Norman
architects generally founded their castles.

The keep of Cardiff Castle is one of the most perfect shell keeps in
existence. It is built on a round artificial mound, surrounded by a
wide and deep moat--the mound and moat being, of course, complements
of each other. Such mounds and moats are common in all parts of
England, and in Normandy. They are not Roman, nor British, nor are
they, as Mr. G. T. Clark maintained, characteristic of Anglo-Saxon
work. They are essentially Norman, and a good representation of the
making of such a mound may be seen in the Bayeux Tapestry, under the
heading--'He orders them to dig a castle.' When was the Cardiff mound
made? Perhaps the short entry in the Brut gives the answer: "1080, the
building of Cardiff began." It would then be surrounded by wooden
palisades, and surmounted by a timber structure, as a newly made mound
would not stand the masonry. The shell keep was probably built by
Robert of Gloucester, and it was probably in the gate-house of this
keep, that Robert of Normandy was imprisoned. A shell keep was a ring
wall eight or ten feet thick, about thirty feet high, not covered in,
and enclosing an open courtyard, round which were placed the
buildings--light structures, often wooden sheds, abutting on the ring
wall--such as one may see now in the courtyard of Castell Coch. The
shell keep was the centre of Robert's castle, but not the whole. From
this time dated the great outer walls on the south and west--walls
forty feet high and ten feet thick and solid throughout. The north and
east and part of the south sides of the castle precincts are enclosed
by banks of earth, beneath which, the walls of a Roman camp have
recently been discovered. These banks were capped by a slight
embattled wall. Outside along the north, south and east fronts was a
moat, formerly fed by the Taff through the Mill leat stream which ran
along the west front. The present lodgings, or habitable part of the
castle built on either side of the great west wall, date mostly from
the fifteenth century. The earlier lodgings were, perhaps, on the same
site--though only inside the wall; a great lord did not as a rule
live in the keep, except in times of