The westernmost bay of the nave has been formed into a kind of =vestibule= by means of the archways constructed, during the last century, to strengthen the towers at that end. The vestibule is in three compartments, two of which, under the western towers, are square. The centre one is the most interesting, since it preserves to us a portion of the first bay of Remigius' nave. High up in the side walls is a Norman arch, part of the original clerestory. Below this we can trace the outline of a wider arch (now filled in), which belonged to the triforium. Considerable alterations were made in these walls by Treasurer Welburne in the second half of the fourteenth century, and the arches were filled in during the early part of the eighteenth century, owing to the instability of the towers. The arch dividing the vestibule from the nave was constructed by an architect named John James (apparently not James Gibbs, as some have supposed) about the year 1730, and altered by James Essex thirty or forty years later. In the time of Bishop Grosseteste (1235-53) the side walls were carried above the Norman clerestory to the height of the present nave, and covered with the characteristic lattice-ornament which we have already seen in the central arch outside. The great west window was also inserted in Grosseteste's time, as well as the cinquefoil window above. The tracery now filling the former is in the Early Perpendicular style, and dates from the end of the fourteenth century. From the broad sill of this window a good view of the interior can be obtained, and a much finer one still from the passage which runs beneath the other window above. From the latter position we have an uninterrupted view of the entire length of the minster, which looks longer than it really is, from the fact that the vaulting is carried at an almost uniform height throughout. [Illustration: Elevation of One Bay on the North Side of the Nave.]