§ 24. But the most interesting case of an external chapel is the Sylvester chapel at Burford, which now forms a long arm stretching to the south-west of the main fabric. The church and chapel were originally separate. The church was, to begin with, an aisleless twelfth century structure, with a tower between nave and chancel. In the thirteenth century the chancel was produced to its present length, the north and south walls of the tower were pierced with arches, and transeptal chapels were added. A narrow south aisle was also added to the nave. About the same time a long aisleless chapel was built in the churchyard, some yards to the south-west of the church. In the fourteenth century a chapel was constructed, with a bone-crypt beneath it, west of the south transept, and was connected with the south aisle. There seems to have been no north aisle to the nave. East of the transepts were small chapels. The fifteenth century saw a great transformation. A sacristy was built north of the altar. Aisles and a south porch of great beauty were built in harmony with a new nave arcade. The outer chapel, the axis of which was not parallel to that of the nave, was prolonged eastward to meet the south porch, and connected by an arcade with the south aisle. It was shortened at the west end, but still projects two bays beyond the main body of the church. The east chapel of the south transept was now taken away, and a south chancel chapel built, the east wall of which interfered with the thirteenth century sedilia of the chancel. The south wall of the chancel, opposite the sacristy, was allowed to stand clear of the new chapel. On the opposite side of the church, the north transept was shortened, until it was little longer than the breadth of the north aisle: its north wall was then continued eastwards and was returned to join the west wall of the sacristy. The north chapel of the chancel was thus formed. The whole progress of the plan is from a simple form of aisleless church to an aisled rectangle with central tower and spire; but the process is irregular, and the absorption of the outer chapel is an almost unique step. It will be noticed that the south aisle is entirely covered by a triple arrangement of buildings--first, St Thomas' chapel next the south transept, then the south porch, and finally the Sylvester chapel, which gives additional length to the church from this point of view. [Illustration: Fig. 3. Plan of Burford Church.]