Bankside, London

The recent opening of the Switch House extension to Tate Modern has been one of this year's most anticipated architectural commissions. It's also helped to complete a public space and a new public route we envisioned more than a decade ago. Herzog and de Meuron's expanded gallery now embraces both front and back, framing a new Bankside piazza and opening up a walkable route from Southwark to St Paul's and beyond.

Tate Modern's immediate neighbours are a collection of three buildings designed by Allies and Morrison - The Bluefin Building, Bankside 2 and Bankside 3. In concert with the Tate, the ensemble creates new routes and generous public spaces in a prime central London location. Walking around the area today, it's hard to imagine that as recently as the late 20th century, this has long been a forgotten place, one just right on the edge, a servant and an appendage to the city rather than its heart. That a power station was situated here is telling.

Much of this place was occupied by, what was once, the largest office building in Europe - St Christopher's House. It was a single monolithic structure, following no particular building line, with no activity on its ground floor, and most significantly, it was completely impermeable along its entire 235 metre length. Fast-forward to today and we have a well-connected, vibrant, purposeful and valuable part of London.

Bankside's success in 2016 is in large part due to its embrace of permeability in the absence of any overall plan. The area's developers took on the responsibility to make a more urban place, to listen to and engage with the surrounding area. This was good business. People want to be in more animated places. The buzz attracts the right tenants and it lifts land values. We worked with Bankside's developers to stitch together routes, to create new open spaces, both north-south and east-west, animated at street level with engaging retail offer. Three new buildings, interesting but not overpowering, complete the piece. Here, the spaces in between matter as much as the buildings themselves.

Landscaped and shaded by trees, today's Canvey Street now melds seamlessly into a new open space before the Tate Modern Switch House. The incidental result is two separate places now joined together as one public space - unplanned in one sense, yet carefully orchestrated in another. Pan out a bit further, one can discern a new pedestrian route that links across to the other side of the River Thames. Today, one can walk from St Paul's, down Peter's Hill, cross the river on Millennium Bridge, and (during Tate Modern's opening hours) walk through the Museum's dramatic public ground floor galleries, out into the new Bankside piazza. Progress south a bit further, and one reaches Southwark Street, to Allies and Morrison's studios. It doesn't end here. As a landlord, we have intentionally kept a public route open on Farnham Place to further extend the walkable link, which continues the route deeper into Southwark.

Without any kind of masterplan, a new public square facing the world's largest museum of modern art has been created, and a pedestrian route has been formed linking historic St Paul's Cathedral on the north bank with Union Street to the south. This 1.2km connection has been made possible through a series of individual initiatives in which one developer will link to the conclusion of the last. They've all engaged in a sort of placemaking medley. and there have been many players in its orchestra: Bankside 123's proprietors, the Tate, those who built the Millennium Bridge, and then our own practice. Each has participated in an iterative and evolving urban plan to compose a better city.