<P> The Palmerston Forts that encircle Portsmouth were built in response to the 1859 Royal Commission dealing with the perceived threat of a French invasion . The forts were intended to defend the Dockyard in Portsmouth . Construction was carried out by the Royal Engineers and civilian contractors (under Royal Engineer supervision). In addition to the newly constructed forts, extensive work was carried out on existing fortifications . </P> <P> The Portsmouth defences can be split into four distinct groups of forts, comprising four sea forts built in the Solent, a group of forts on Portsea Island, a group of forts along Portsdown Hill overlooking Portsmouth, and a group of forts on the Gosport peninsula . </P> <P> As well as these forts surrounding Portsmouth, further protection for Portsmouth was provided by additional Palmerston forts on the Isle of Wight . </P>

How many forts are there in the solent