Sir Arthur (who would also become an Irish MP) became a General in the armies of King William III during the Jacobite War in Ireland. He was quickly besieged in Derry, but managed to escape. After the war, with the Protestant Ascendancy of which he was a part yet again restored, Sir Arthur (who had presumably profited greatly from the war) returned to Moira. Having inherited the brick manor house his father had purchased he decided to expand it greatly, and it became one of the largest residences in the whole island, to be called Moira Castle. The castle, which in fact was a mansion, was also accompanied by vast gardens. These gardens became world-famous. In 1690 Sir Arthur utilised his friendship with fellow Down-born botanist Sir Hans Sloane, and acquired from him the seeds of 400 exotic plants, and instructions in how to grow them. To fit his ends Sir Arthur also constructed in Moira the first hothouse in Europe.