Raglan Castle may have originated as a motte-and-bailey castle when the Normans conquered Gwent in the late eleventh century.
Around 1435 Sir William ap Thomas, a veteran of the French wars, started work on the present structure. He built the Great Tower, a massive, moated keep-like structure that could only be approached from within the castle itself. In 1461, after the death of Sir William, his son William Herbert became Baron Herbert of Raglan and embarked on a lavish and ambitious building programme to reflect his new status. He developed suites of accommodation around the Fountain Court, built the Pitched Stone Court, and constructed the gatehouse to both impress and intimidate visitors to the castle. However, by his execution in 1469, the work was unfinished and was not until the castle passed to the Somersets, earls of Worcester, that Raglan underwent its final transformation. William Somerset, the third Earl of Worcester, remodelled the hall range, built a long gallery and extended the Pitched Stone Court. He also created a garden with long walled terraces and a lake. After his death his son continued to enhance the garden with a water parterre and bedecked the moat walk with statues of Roman emperors. Unfortunately, the castle experienced deliberate destruction during the Civil War as the castle was besieged for ten weeks in 1646 by parliamentarian troops.
Source: Kenyon, J.R. 2003. Raglan Castle: CADW
M. Lloyd Davies, RCAHMW, 22 October 2008