Catherine was the aunt of Charles V, the Holy Roman Emperor, who took the annulment as a personal insult. This resulted in France and the Empire declaring an alliance against Henry in 1538, and the Pope encouraging the two countries to attack England. An invasion of England appeared certain. In response, Henry issued an order, called a "device", in 1539, giving instructions for the "defence of the realm in time of invasion" and the construction of forts along the English coastline. The immediate threat passed, but resurfaced in 1544, with France threatening an invasion across the Channel, backed by her allies in Scotland. Henry therefore issued another device to further improve the country's defences, particularly along the south coast. The castle was built on the southern end of Portsea Island to protect a deep-water channel running through the Solent to the royal naval base at Portsmouth. Work began in early 1544, under the overall direction of Sir Anthony Knyvett, the Governor of Portsmouth, supported by Richard Cawarden, the Dean of Chichester, and John Chatterton, the captain of the Portsmouth garrison; Thomas Bertie was appointed as the master mason. It is uncertain who designed the castle, although Knyvett described it as being "of his Majesty's own device", which typically indicated that the King had taken a personal role. The design abandoned the earlier use of semi-circular bastions, which could not be fully covered by flanking fire from the supporting walls, and instead used an angular design, forming an early, if imperfect, adoption of the "trace italienne"-style of fortification already in use in Continental Europe. The work was carried out quickly due to the risk of a French attack, and by July two brass saker guns were mounted on the site. It cost at least £3,100, £1,300 of which came from the proceeds of the Dissolution of the Monasteries, with chalk, stone and timber being brought across from the neighbouring Isle of Wight. The castle was completed by October and formed a fortification with a square keep, rectangular gun platforms to the east and west, and angled bastions to the front and rear. Chatterton was appointed the new captain, with a team of eight soldiers, twelve gunners and a porter. The castle was well-armed, with seven brass artillery pieces - a culverin, demi-culverin, cannon and demi-cannon - and eight iron guns.