the regional rise of major noble families such as the Percies and the Nevilles, whose wealth encouraged a surge in castle building at the end of the 14th century. New castles at Raby, Bolton, and Warkworth Castle took the quadrangular castle styles of the south and combined them with exceptionally large tower keeps to form a distinctive, northern style. Built by major noble houses, these castles were typically even more opulent than the smaller castles like Nunney, built by the nouveau riche. They marked what historian Anthony Emery has described as a "...second peak of castle building in England and Wales," following on from the Edwardian designs at the end of the 14th century. In the 15th century, the fashion for the creation of very expensive, French-influenced palatial castles featuring complex tower keeps spread, with new keeps being built at Wardour, Tattershall, and Raglan Castle. In central and eastern England, some keeps began to be built in brick, with Caister and Tattershall forming examples of this trend. In Scotland, the construction of Holyrood Great Tower between 1528 and 1532 drew on this English tradition, but incorporated additional French influences to produce a highly secure but comfortable keep, guarded by a gun park. These tower keeps were expensive buildings to construct, each built to a unique design for a specific lord and, as historian Norman Pounds has suggested, they "...were designed to allow very rich men to live in luxury and splendour." At the same time as these keeps were being built by the extremely wealthy, much smaller, keep-like structures called tower houses or peel towers were built across Ireland, Scotland, and northern England, often by relatively poorer local lords and landowners. It was originally argued that Irish tower houses were based on the Scottish design, but the pattern of development of such castles in Ireland does not support this hypothesis. A tower house would typically be a tall, square, stone-built, crenelated building; Scottish and Ulster tower houses were often also surrounded by a barmkyn or bawn wall. Most academics have concluded that tower houses should not be classified as keeps but rather as a form of fortified house. As the 16th century progressed, keeps fell out of fashion once again. In England, the gatehouse also began to supplant the keep as the key focus for a new castle development. By the 15th century, it was increasingly unusual for a lord