As well as the forts surrounding Portsmouth, further protection for Portsmouth was provided by existing and new defences on the Isle of Wight. The Portsmouth defences can be split into four distinct groups. The first are the four forts built in the Solent. These sea forts were designed to protect the eastern approaches to Portsmouth Harbour. * Spitbank Fort * St Helens Fort * Horse Sand Fort * No Mans Land Fort The second group are those actually on Portsea Island. None of these were built as a result of the 1859 Royal Commission but did receive improvements because of it.