This is part of a series of posts about Wren’s masterplan for rebuilding London after its Great Fire destroyed most of the City of London in 1666 and also the ideas that the masterplan sparked. They are published in the hope that they might prove thought-provoking and in the hope that flaws in observation and argument might be identified and corrected.
Lesson 1. Optical perspective influences how we perceive landmarks: use it to support the design’s intention, tooth not undermine it
On Wren’s masterplan for the reconstruction of London after its Great Fire in 1666, St. Paul’s Cathedral seems to be a dominating presence. Coming in from Ludgate the Cathedral would be immediately apparent as it not only sits atop Ludgate Hill but guards the space where two of the three great arterial streets diverge.
That Wren intended the new cathedral that he was destined to design to be a dominant and monumental feature of London is emphasised by his decision to flank the entrance to the cathedral with two comparatively tiny parish churches. These surely cannot plausibly be there to serve some catchment area as they are so close to each other and to the cathedral. I assume that they are there simply to emphasise the Brobdingnagian size of the cathedral through their relative tininess. If it is indeed Wren’s intention to make the Cathedral look vast, then his intention seems to be fundamentally undermined by one of the very mechanisms he presumably used in the hopes of imparting it great significance: its location in the street layout.
By placing St. Paul’s at the base of a huge triangular piazza Wren would make St. Paul’s look to someone approaching it significantly smaller than it actually is. This is because key to our perceptions of whether an object is small or merely distant is the cues given by perspectival recession – the way lines stretching out into the distance tend to look like they are converging, as with rail tracks apparently meeting at a distant point despite being entirely parallel.
This optical illusion can be manipulated to achieve a couple of effects. Firstly, if instead of running parallel lines towards a building we use lines that are in fact converging anyway then the optical illusion is emphasised, making the building seem (let’s say) 150m away when it is actually only 100m away. This encourages the eye to ‘read’ the building as being the size it would be if it were 150m away: i.e. it fools us into thinking that it is larger than it actually is.
The reverse is also true: where the lines physically diverge into the distance towards an object then the effects of perspective are counteracted, making the building seem closer than it really is, and therefore smaller.
The diverging lines of the second picture counteract the tendency for lines to converge to a vanishing point, making the lines seem almost parallel rather than converging. This encourages us to think that the vertical object in the second picture is much closer than in the first picture where the receding lines are pronounced. In fact, of course, the two vertical objects are identical. The only difference between the two pictures is that in the first picture the lines converge to the edges of the vertical object at an angle of 9 degrees each side, whilst in the second the lines diverge from the same baseline, also at an angle of 9 degrees each side. The angle of 9 degrees each side is used because that is the divergence used by Wren in his streetplan.
Perspective tricks are used everyday to play with perceptions of landmarks whose size is well-known, most famously at the Leaning Tower of Pisa, so it’s no surprise that the designers of public spaces also use them.
For example, the ‘Potemkin Stairs’ in Odessa were clearly designed to produce particular optical effects — from the top of the staircase, the steps are invisible and all you can see are the landings; from the bottom the landings are invisible and all you can see are steps. The 142m long staircase is so designed that the bottom step is significantly wider at 21.7m than the top step at 12.5m. This subtle convergence (at about 2 degrees from parallel on each side) reinforces the normal perspectival recession and makes the staircase seem longer than it really is.
In addition to this monumental staircase this effect has been also utilised in two of the greatest of piazzas: San Marco’s in Venice, and Michelangelo’s Campidoglio in Rome.
Piazza San Marco, Venice
Piazza San Marco is essentially trapezoid, as is its Piazzetta that links it to the Grand Canal. The wide end of the main square terminates with St. Mark’s Basilica; the tapering sides, hosting the administrative offices of the old Republic, stretch towards the opposite end.
The effect of the two long sides of the piazza diverging (by about 12 degrees from each other) is to seem to reduce the vast bulk of the Basilica when seen from the opposite end of the trapezoid.
Conversely, if we stand near the entrance to the Basilica with our backs to it then the length, and therefore size of the administrative offices are exaggerated.
Placing the piazza’s most important single building at the wide end of the trapezium is a fundamentally egalitarian move that, at the same time as it gives the Basilica pride of place in the square, also asserts the importance of the buildings on the flanks — and their government functions. In so doing, it celebrates both. In effect, ‘Render unto God what is God’s, but render unto the Republic what is the Republic’s.’
In what might conceivably be an example of that rare thing, the street layout joke, the effect is reversed in the adjoining Piazzetta. The sides of the Piazzetta — taken up by the Doge’s Palace on one side, and the Mint and Library on the other, converge as they point towards the Palladio-designed church of San Giorgio Maggiore.
The convergence is only by a few degrees, and the bulk of the distance between the Piazzetta is taken up by the Grand Canal so the effect is rather subtle, but in making the church loom somewhat larger relative to its actual size, the sides of the Piazzetta have the opposite effect to the main piazza: the Republic’s buildings are diminished, that of God emphasised.
Whilst the Piazzetta does not precisely point towards San Giorgio Maggiore – the island isn’t quite in the right place, and San Maggiore was developed centuries after the Piazzetta – the uncanny architectural similarity of the belltowers of San Marco and San Giorgio Maggiore surely demonstrate an intent to relate the two churches and their settings.
The Campidoglio, by Michelangelo
Michelangelo also made use of this perspectival device in his design for the Piazza del Campidoglio on the Capitoline Hill in Rome. As we arrive in the piazza from Michelangelo’s staircase the Senate building is in front of us at the wide end of the piazza and two palaces of lesser height are at the sides.
One effect of these diverging sides is that the Senate building seems less dominating of the square than it otherwise would. The piazza seems almost square, and the differences in height between the side buildings and the palace at the back are minimised.
The other effect I’d like to mention is that with our backs to the Senate the converging sides of the square encourage our eyes to look into the distance roughly in the direction of the Vatican. (I believe part of Michelangelo’s brief was to change the orientation of the buildings on Rome’s most important hill from facing the pagan Forum to the Christian Vatican.)
Wren’s Plans for a Piazza in front of St. Paul’s
Returning to Wren’s design for the piazza before St. Paul’s, by placing the cathedral at the wide end of the long triangular piazza whose sides show strong divergence (roughly 9 degrees each side of the centre) he would have greatly diminished the imposing monumentality of the cathedral and boosted the relative importance of the buildings on the sides of the piazza. This, as we have seen, is not necessarily such a bad thing, but the buildings on the sides seem, on the basis of the design, to have no particular reason to be so inflated in importance, and indeed as noted the only marked buildings on the sides — the tiny parochial churches — seem to be designed to boost the relative size of the cathedral rather than the reverse.
It seems, then, that the aggrandisement of St. Paul’s through its position on the streetplan is profoundly counterproductive. Wren may have had reasons to do this — by making St. Paul’s seem closer it may be more inviting for people to walk there; by having the streetplan undercut the status of the Cathedral it might suit the supposed British national characteristic of a fondness for both pomp and the mocking of that pomposity — but I’m scrabbling around for an explanation here. If any reader has any idea what Wren might wish to achieve here, and how his design supports that aim then I’d be delighted to hear it.
Where it is desired to lessen the physical dominance of one building over others in a piazza, one technique is to make the sides of the piazza diverge as they lead towards that building; where it is desired to emphasise that building converging sides may be used.
Where one side of a piazza is left open in order to provide a vista, as in San Marco’s Piazzetta or Michelangelo’s Campidoglio, the use of piazza sides that converge in the direction of the vista can provide ‘leading lines’ that may help imply a relationship between the piazza and some landmark in the distance, for example the Vatican or San Giorgio Maggiore.