Read this: With the wealth brought on by the gold rush following closely on the heels of the establishment of Victoria as a separate colony and the subsequent need for public buildings, a program of grand civic construction soon began. The 1850s and 1860s saw the commencement of Parliament House, the Treasury Building, the Old Melbourne Gaol, Victoria Barracks, the State Library, University, General Post Office, Customs House, the Melbourne Town Hall, St Patrick's cathedral, though many remained uncompleted for decades, with some still not finished.
Now answer this question, if there is an answer (If it cannot be answered, return "unanswerable"): During what two decades were the Parliament House, Treasury Building, Victoria Barracks, State Library, and General Post Office commenced?
1850s and 1860s