In around 1770 the neoclassical architect Robert Adam designed Pulteney Bridge , a three @-@ arched bridge spanning the River Avon . He used as his prototype an original , but unused , design by Andrea Palladio for the Rialto Bridge in Venice . Adam also submitted plans for the new Assembly Rooms but these was rejected as too costly . John Wood , the Younger raised funding for the construction of the Assembly Rooms by the use of a Tontine , an investment plan that is named after the Neapolitan banker Lorenzo de Tonti , who is credited with inventing it in France in 1653 . It combine features of a group annuity and a lottery . Each subscriber pay an agreed sum into the fund , and thereafter receive an annuity . As members die , their shares devolve to the other participants , and so the value of each annuity increases . On the death of the last member , the scheme is wound up . Construction started in 1769 and was completed in 1771 , when a grand opening was held .