Other remains of this date are somewhat scattered. Two windows in the undercroft of Bishop Bek's, or what is now known as Bishop Hatfield's Hall, are examples. They have converging jambs, the semi-circular heads being cut from one stone and the inside very widely splayed. The wall from the keep to the chapel, and that from the keep to the gateway are also Norman work, as are also portions of the gateway itself.

The next important changes in the castle were made by Bishop Pudsey, 1153-1195, who not only repaired the existing work but built a hall, known as Pudsey's Hall. Although this hall has now almost entirely disappeared, through repairs and alterations, sufficient evidence as to its whereabouts and general plan is forthcoming. It was of two storeys, the lower and upper halls. Entrance to the lower hall was originally gained by a staircase which led from the courtyard to the splendid doorway now enclosed in Tunstall's Gallery. This magnificent entrance having been covered with lath and plaster, and for long completely forgotten, was unearthed by, and at the expense of Bishop Barrington, early in the present century. It is in good preservation and is a splendid specimen of rich Norman architecture. It consists of five orders, all richly carved and moulded. Three orders rest on carved capitals and shafts, and two are carried down the jambs of the doorway. The stairway has entirely disappeared, but there is little room to doubt that it would be of much the same character as that in the close at Canterbury; and to the protection afforded by the staircase roof, we are, no doubt, indebted for the good preservation of the arch mouldings of the doorway itself.

What was originally Pudsey's Upper Hall is now styled the Norman Gallery. The greater portion of this gallery is at the present time divided into chambers of residence for the students of the university. It is reached by the Black Staircase and a doorway in the Early English Gothic style. The interior of the south and west walls are enriched by arcades in groups of three, the central bay of each of which is larger than those flanking it, and is pierced by a window. The arches of the arcade rest on shafts and cushion capitals, and are carved with chevron ornament. The whole arrangement hereabouts bears the impress of having been a portion of one great building, which an examination of the roof, lead, and general outline makes even more certain.

On the western side of the courtyard stands the great Bek's Hall, built by the bishop of that name. It is above the Norman undercroft, previously mentioned. Much of its original character is now lost, owing to restorations, curtailments, and alterations. Bek's doorway is still in existence, though much hidden by the porch erected later by Bishop Cosin. It has a pointed arch of two orders, with detached shafts in the jambs. Another original relic, unrestored, is part of the window nearest the fireplace, which is valuable as evidence of the date of the erection of the hall. The tracery is geometrical, and the shafts in the angles of the splays are banded. About the year 1350 Bishop Hatfield enlarged and altered Bek's hall. At the west end he inserted two light windows, which are now blocked, though the tracery may be seen from students' rooms inside, and partly from the outside. The open oak roof, with the exception of some necessary later repairs, is of Bishop Hatfield's time. Hatfield repaired and altered Pudsey's upper hall by the addition of east and west windows, and probably a new roof. He also rebuilt the Keep, which time and war had greatly injured. The existing keep, which was erected in 1840, is similar to Hatfield's, and in many places stands upon the old foundations. It is now used entirely as apartments for students of University College.

Bishop Fox (1494-1501) is responsible for the next important changes. He curtailed the great hall by a partition wall near its south end, which still exists. The wall bears his badge in two places—a pelican feeding her young with blood from her breast. He also adapted part of Pudsey's buildings, near the south-west corner of the castle, to the purposes of a kitchen, erected three fireplaces, and windows, and the oak buttery hatch which opens from the kitchen, and which again has carved upon it "the pelican in her piety."

Bishop Tunstall (1530-1558) built Tunstall's Gallery, which extends from the great hall to the clock tower. It is entered by Cosin's staircase (erected later) and by an eastern stair built by Tunstall himself. A curious feature of this stairway is a port-hole which commands the main entrance to the courtyard. The present beautiful little chapel is also the work of Bishop Tunstall. It contains some notable carved oak stalls, of earlier date than the chapel itself, which were brought from the castle at Bishop Auckland. The carved devices of the miserere seats of these stalls are curious and worthy of attention. The doors in the gateway of the courtyard are the work of Tunstall's time.

Bishop Cosin (1660-1672) found the castle in a dilapidated condition. During the Commonwealth it had been sold to the then Lord Mayor of London, who used it badly, to say nothing of the ruin caused by the Scots. He spent large sums in its restoration. He added the present porch or entrance from the courtyard to the great hall. The great staircase in the north-west corner of the courtyard is his and bears his arms. Within and leading to Tunstall's Gallery is the Black Staircase, also the work of Cosin. He enlarged the chapel, and constructed and fitted several apartments in the castle, besides several minor works. In his will, he says, he spent the greater part of his temporal estate in "rebuilding and repaireing the two episcopall Castles of Durham and Bishop Auckland." This, he states, cost him seventeen thousand pounds, including the furnishing and ornamenting of the chapels, which he did "for the use of my successors in those Chappells for ever." Many of the agreements between Bishop Cosin and his masons, plasterers, carpenters, and painters, from which the exact dates and prices paid for the work may be learned, are preserved.

The latest important work at the castle was the rebuilding of the keep, in 1840, which was described at that time as "a picturesque ruin." It was entirely rebuilt on its original plan. The gateway to the courtyard was repaired and modernised by Bishop Barrington, with the existing inartistic result.

Durham Castle owes its picturesque appearance to two causes—first, its magnificent and commanding position, on a rocky escarpment; and second, no doubt, to the many vicissitudes through which it has passed, the alterations and additions made necessary by time and constant war, and later, the entirely different uses to which the building is put.