Complex sentence: A previous bridge on the site, designed by John Rennie, opened in 1819, (originally Known as Queen Street Bridge, as shown on the 1818 John Snow Map of London) consisted of three large cast-iron spans supported by granite piers.
Split into simpler sentences: A previous bridge on the site, designed by John Rennie, opened in 1819, and was originally known as Queen Street Bridge, as shown on the 1818 John Snow Map of London. The bridge consisted of three large cast-iron spans supported by granite piers.