Building From 1769
The first bridge on this site (shown in the picture) was designed by Robert Mylne and added a third crossing point to those already provided by London Bridge and Westminster Bridge. The plaque says 1760 but it took so long to build that it did not open until 1769, just at the end of Pitt the Elder's term as PM so it was named after him.
The location was chosen because there was available a wide route leading from the river up to what is now Ludgate Circus. This was the River Fleet with its disused wharves on both banks. It became the wide New Bridge Street. The equivalent road on the south bank crossed mainly open fields to the new St George's Circus.
Faulty workmanship meant the bridge needed replacing and this new bridge was opened by Queen Victoria on 1869. The bridge is dedicated to her, hence the statue on the north bank. Stone carvings of water birds by John Birnie Philip. Bridge designed by Joseph Cubitt, son of Sir William. Joseph also designed the sister rail bridge. The road bridge was widened 1907–10.
In Google Satellite view you can see, reading left to right: Cubitt's road bridge, Cubitt's 1864 railway bridge piers (the bridge itself was removed 1985), the 1886 bridge which has recently (2014) been converted to carry Blackfriars Station platforms. Note how the piers on all three bridges line up, presumably to ease passage for shipping.