Complex sentence: By the time the first Fencibles arrived in 1848 the rebels in the north had been defeated so the outlying defensive towns were constructed to the south stretching in a line from the port village of Onehunga in the West to Howick in the east.
Split into simpler sentences: By the time the first Fencibles arrived in 1848, the rebels in the north had been defeated. Outlying defensive towns were then constructed to the south, stretching in a line from the port village of Onehunga in the West to Howick in the east.