St Paul's Cathedral was rebuilt after the Great fire of London in 1666 by Sir Christopher Wren. Wren presented several designs before the final one was agreed ... This plan received the Royal Warrant in May 1675, and is therefore known as the Warrant Design  ... Fortunately, it was allowed that Wren would have 'the liberty, in the prosecution of his work, to make some variations, rather ornamental than essential, as from time to time he should see proper' ... He certainly took advantage of this licence, and was liberal in calling ornamental what he considered essential. ... On 21 June 1675 the first stone was laid at the E end. There is no sign of any second thoughts thereafter ... Rather than build in stages (e.g. east to west, as was common), he laid foundations for every part as quickly as possible: another safeguard against parsimonious meddling or partial completion. ... The dome was finished in 1708 and the whole building declared complete by Parliament in 1711. The chief material was of course Portland stone ... Wren had been thirty-four at the time of the Fire; he was seventy-nine in 1711. ...

The first alteration made by Wren between Warrant Design and execution concerned the disposition of the outer walls. This was to affect the appearance of the whole building. The Warrant Design had a nave with clerestory and lower aisles like a medieval English cathedral. In the execution Wren carried up the outer aisle wall to nave height, as a screen wall - that is, he erected an outer two-storey elevation, the upper section of which was wholly make-believe. In this Wren established himself at once as a man of the Baroque and not of the Renaissance. The high outer walls add dignity to the whole structure and act as a broad unbroken podium for the all-dominating dome. Additionally, they help to buttress the thrust of the main vault. When one looks down from the dome behind these walls, a row of flying buttresses also appears on each side. Wren did not mind using this medieval method of counteracting the thrust of the vaults, as long as it was not normally evident to the eye. ...
The wall is rusticated and there are coupled pilasters on both floors, Composite over Corinthian. The lower storey has a round-headed window in an eared frame with scrolled keystone, and garlands and cherubs' heads above. The upper storey has a blank window with a niche in an aedicule with Composite columns and a pediment. Below the blank window in the base of the aedicule a real window appears, lighting the roof space over the aisle vaults and invisible from the aisles below. ... A balustrade finished the unit, in 1717-19. Wren would have preferred a solid parapet, but his Commission insisted. He was cross about it and said: 'Ladies think nothing well without an edging'.  Stylistically the origin of the unit as a whole is the Banqueting House and Inigo Jones's and John Webb's Palladianism altogether. ...

West Facade ... In the middle is a two-storeyed portico of coupled columns ... In this portico again Wren's affinity with the Continental Baroque is obvious. On the ground floor there are six pairs of columns, on the first floor only four, i.e. the outer pairs below merge with the bays belonging to the towers, in line with the coupled pilasters of the W wall ... The four central pairs carry the free-standing columns of the first-floor balcony. ... 

Above is a pediment with a relief of the Conversion of St Paul ... (1706) by Francis Bird, a fine composition of several mostly mounted figures. It catches something of the drama of Bernini's famous equestrian statue of Constantine in the Vatican, which Bird must have seen. ...

North-west tower from the north, and detail of the ground floor on the west side.  South-west tower with supporting upper storey from the south, and detail of ground floor south window.
The WEST TOWERS are the broadest, most substantial and most Baroque of all Wren's spires. Above the sturdy clock stage they turn round, with pairs of columns carrying straight entablatures projecting in the diagonals, and convex sections with pairs of matching columns between them. Three further stages with urns and complex volutes lead up to an octagonal lantern and an ogee cap with gilt pineapple finial. The stone structure is mostly open, so the whole is much more intricate than this description can convey. ...

The Dome. It is in the most telling contrast to the W front - though not well seen from there - achieving a final repose far more convincing than St Peter's, where the 'slancio' upward never ceases. Wren, just as he relished variety in his City churches, could consciously develop this contrast between Baroque dynamics and an ultimate end in peace and harmony. The base of the drum below the colonnade is left entirely plain. The drum with its peristyle is a direct descendent of Bramante's unexecuted design for St Peter's, illustrated by Serlio ... (but) Wren even here betrays his his faith in the style of a different century. Bramante intended an even colonnade all round his drum. Wren's is not even. In eight places the columns do not stand free, but pieces of wall reach out towards them and appear adorned with niches, between them. The reason is structural and also practical (they house staircases), the effect Baroque - though mildly so by comparison with the towers. The infill is tawny Ketton stone, which keeps the Portland stone columns visually discrete. Above the peristyle is a balustrade, and then the drum rises yet higher, carrying on the diameter of the wall behind the colonnade. This attic has near-square windows. Above this at last follows the dome. It is of an elongated section, but so much less so than e.g. St Peter's that from almost any viewpoint it seems a perfect hemisphere. What makes Wren's dome also look more at rest than the dome carried out at St Peter's, probably to Michelangelo's design, is the absence of lucarnes and the extreme shallowness of the ribs. The ribs of the dome of St Peter's lead the eye upward all the time. At St Paul's the crowning lantern is a glorious and indeed decidedly Baroque design with pairs of coupled columns projecting on the four sides, an upper stage with a little dome, and a ball with cross - all no more than a final weight on the dome, heavy enough and not too heavy. ...  St Peter's (external site)

Pictures taken just inside the west end, showing the north aisle, a glimpse of the nave, and the north-west chapel off the north aisle. Regrettably, beyond this point photography was not permitted. Virtual Tour at external website.

St Paul's Cathedral Website