The statuary of the Chartres portals is considered among the finest existing Gothic sculpture. One of the few parts of the cathedral to survive the 1194 fire, the "Portail royal" was integrated into the new cathedral. Opening on to the "parvis" (the large square in front of the cathedral where markets were held), the two lateral doors would have been the first entry point for most visitors to Chartres, as they remain today. The central door is only opened for the entry of processions on major festivals, of which the most important is the "Adventus" or installation of a new bishop. The harmonious appearance of the façade results in part from the relative proportions of the central and lateral portals, whose widths are in the ratio 10:7 – one of the common medieval approximations of the square root of 2. As well as their basic functions of providing access to the interior, portals are the main locations for sculpted images on the Gothic cathedral and it is on the west façade at Chartres that this practice began to develop into a visual "summa" or encyclopedia of theological knowledge. Each of the three portals focuses on a different aspect of Christ's role in salvation history; his earthly incarnation on the right, his Ascension or existence before the Incarnation on the left, and his Second Coming (the Theophanic Vision) in the centre. Above the right portal, the lintel is carved in two registers with (lower) the Annunciation, Visitation, Nativity, Annunciation to the Shepherds and (upper) the Presentation in the Temple. Above this the tympanum shows the Virgin and Child enthroned in the "Sedes sapientiae" pose. Surrounding the tympanum, as a reminder of the glory days of the School of Chartres, the archivolts are carved with some very distinctive personifications of the Seven Liberal Arts as well as the classical authors and philosophers most closely associated with them. The left portal is more enigmatic and art historians still argue over the correct identification. The tympanum shows Christ standing on a cloud, apparently supported by two angels. Some see this as a depiction of the Ascension of Christ (in which case the figures on the lower lintel would represent the disciples witnessing the event) while others see it as representing the "Parousia", or Second Coming of Christ (in which case the lintel figures could be either the prophets who foresaw that event or else the 'Men of Galilee' mentioned in Acts 1:9-11).