She was originally built as a large ship of the line, but was converted into a central-battery ironclad while still under construction.

The engines were rated at a total of 1,000 nominal horsepower or 3,700 indicated horsepower (2,800 kW)[2] and gave Sagunto a speed of 12.5 knots (23.2 km/h; 14.4 mph)[1] The ironclad carried a maximum of 900 metric tons (886 long tons) of coal.

[3] She was fitted with a three-masted ship rig with a sail area of 2,400 square meters (26,000 sq ft).

[4] The frigate's main battery was originally intended to consist of thirty 200-millimeter (7.9 in) smoothbore guns mounted on the broadside, but she was completed with eight single Armstrong-Whitworth 229-millimeter (9 in) rifled muzzle-loading (RML) guns on the main deck arranged on the central-battery principle.

[6] Segunto, named for the ancient Siege of Saguntum,[7] was ordered in December 1862 as the 100-gun ship of the line Principe Don Alfonso from the Royal Shipyard of Esteiro (Reales Astilleros de Esteiro) in Ferrol.