Why were heavy World War I artillery pieces transported in separate sections?

During World War I, heavy artillery pieces were transported in separate sections primarily due to the limitations of the motive power available at the time and the immense weight of the weaponry.1

Before the widespread adoption of internal combustion engines, horses served as the standard motive power for field artillery. To move these massive guns, designers had to ensure that each component—such as the barrel, mounting, carriage, and ground platform—could be dismantled into loads that fell within the hauling capacity of a horse team. The gun would then be transported in these individual pieces and reassembled at the firing position.1

Even as motor tractors began to replace horses for heavier artillery, the practice of disassembly continued for the largest weapons, such as the 420-mm howitzers known as "Big Bertha." These guns were split into four distinct units carried on separate wagons, with a fifth wagon carrying a hoist to facilitate assembly at the site. As the war progressed and artillery grew even larger, some pieces became too heavy to be split into convenient road loads, leading to the development of railway mountings to distribute the weight across tracks.1