 The principal , or South façade , is 344 feet ( 104 @.@ 9 m ) in length ( from each of the flanking wings to the other ) , its austerity relieved on the piano nobile level only by a great six @-@ columned portico . Each end of the central block is terminated by a slight projection , containing a Venetian window surmounted by a single storey square tower and capped roof , similar to those employed by Inigo Jones at Wilton House nearly a century earlier . A near identical portico was designed by Inigo Jones and Isaac de Caus for the Palladian front at Wilton , but this was never executed . 
