The hospital was originally conceived in 1848 by a committee of Justices chaired by Sir John Wither Awdry for providing an asylum for the pauper lunatics of the county of Wiltshire alone. Forty-eight acres of land was purchased from Mr THS Southeron at the end of Pans Lane in the parish of Roundway. The cost was raised by loans from the government and other subscribers to be paid back over 21 years. Construction was started in 1849. The architect was Thomas Henry Wyatt, well known for his institutional architecture. The style was Italianate and the first phase cost £19,594. Construction was by T & W Piper, the addition of ironwork by Knight & Co. for railings around the buildings cost a further £1,069. The principal building material was stone from the Murhill Quarries near Winsley and the roof slates came from Wales. The quarries were conveniently placed about 15 miles away along the Kennet and Avon Canal which had opened some 50 years earlier. The slates were likewise transported by canal.