In May 1878, the designs of Joseph Reed and Frederick Barnes were chosen for the Main Building of the Exhibition. On 19 February 1879 Governor Sir George Bowen laid the cornerstone in Carlton Garden for the new Exhibition Building. The building, built by David Mitchell, covered about 7 acres. Its nave measured 500 x 160 feet and the transept was 272 feet long. A large dome 60 feet in diameter rose 217 feet above the building. Two machinery annexes, each 460 x 138 feet, were built at the rear of the main building.