Work began in the early 1850s and was largely complete in the mid-1860s .
Commercial and residential buildings such as Palmeira House and Gwydyr Mansions continued to be added at the northern end throughout the late 19th century .
Work began in the early 1850s and was largely complete in the mid-1860s , although commercial and residential buildings such as Palmeira House and Gwydyr Mansions continued to be added at the northern end throughout the late 19th century .