The plan consists of a nave and aisles of five bays, a transept projecting one bay beyond the aisles, and three apses to the east. At the crossing the vault is slightly raised so as to admit of four small round windows opening above the flat roofs of the central aisle and transepts. The only peculiarity about the plan lies in the two western towers, which near the ground are squares set diagonally to the front of the church and higher up change to octagons, and so rise a few feet above the flat roof. About the end of the fifteenth century two small chapels were added to the north of the nave, and later still the spaces between the buttresses were filled in with shallow altar recesses.
The likeness to Batalha is best seen in the Capella Mor. As the apse has only three instead of five sides, the windows are rather wider, and there are none below, but otherwise the resemblance is as great as may be, when the model is of fine limestone and the copy of granite. The buttresses have offset string courses, and square crocketed pinnacles just as at Batalha; there has even been an attempt to copy the parapet, though only the trefoil corbel table is really like the model, for the parapet itself is solid with a cresting of rather clumsy fleurs-de-lis. These pinnacles and this crested parapet are found everywhere all round the church, though the pinnacles on the aisle walls from which the plain flying buttresses spring are quite different, being of a Manoelino design. Again the north transept door has evidently been inspired by the richness of Batalha. Here the door itself is plain, but well moulded, with above it an elaborately crocketed ogee drip-mould, which ends in a large finial; above this rises to a considerable height some arcaded panelling, ending at the top in a straight band of quatrefoil, and interrupted by a steep gable. (Fig. 38.)
No other part of the outside calls for much notice except the boat-keel corbels of the smaller apses, the straight gable-less ends to transept and nave which show that the roofs are flat and paved, and the western towers. These are of three stories. The lowest is square at the bottom and octagonal above, the change being effected by a curved offset at two corners, while at the third or western corner the curve has been cut down so as to leave room for an eighteenth-century window, lighting the small polygonal chapel inside, a chapel originally lit by two narrow round-headed windows on the diagonal sides. In the second story there are again windows on the same diagonal sides, but they have been built up: while on the third or highest division--where the octagon is complete on all sides--are four belfry windows. The whole is finished by a crested parapet. The west front between these towers is very plain. At the top a cresting, simpler than that elsewhere, below a round window without tracery, lower still two picturesque square rococo windows, and at the bottom a rather elaborate Manoelino doorway, built not many years ago to replace one of the same date as the windows above.