Fort Rowner was designed by
William Crossman to protect Portsmouth. With its formidable firepower, its main purpose was to guard the approach from potential landing areas on the south Hampshire coast. According to the record plans of Fort Grange, the estimated costs of Rowner, Brockhurst and Grange were £300,000 whilst the actual costs were :- Rowner £52,994, Brockhurst £51.514, Grange £60,676, a total of £169,228 charged to the vote and £2,956 to the loan. The contractor was Mr. Piper. During the construction of Fort Rowner in 1861 fractures were discovered in some of the arches of the left flank and keep. The former was reconstructed and tie rods were inserted to remedy the faults in the keep. Forts Brockhurst, Grange and Rowner were designed on the plan of a detached bastion with an obtuse salient. Each fort was excavated from the level, the earth excavated from the ditch being used to build the ramparts and the redan. The three forts were constructed as nearly as possible on a straight line so securing their fronts from the effects of enfilade. They were intended as bastions affording each other mutual support but, as the ditches of one could not be flanked by the other, caponiers were necessary at the angles. Rowner was condemned as faulty by the Inspector of Works and the contractor was fired in 1862. The work was taken over by the Royal Engineers and completed using military labour at a cost of £1,561 to correct the faults. A feature of the three new Gosport Advanced Line forts was the circular keep placed centrally to the rear. It was still argued in military circles that a keep, although considered by some to be an unnecessary hang-over from the medieval period, was still needed to protect the unfortunate survivors of a fort that had been overrun by the enemy from the overzealous excesses of a victorious army. ==Armament==