Almost immediately after Patterson's arrival, lion attacks began to take place on the workforce, with the lions dragging men out of their tents at night and feeding on their victims. Despite the building of thorn barriers (bomas) around the camps, bonfires at night, and strict after-dark curfews, the attacks escalated dramatically, to the point where the bridge construction eventually ceased due to a fearful, mass departure by the workers. Along with the obvious financial consequences of the work stoppage, Patterson faced the challenge of maintaining his authority and even his personal safety at this remote site against the increasingly hostile and superstitious workers, many of whom were convinced that the lions were in fact evil spirits, come to punish those who worked at Tsavo, and that he was the cause of the misfortune because the attacks had coincided with his arrival.
The man-eating behaviour was considered highly unusual for lions and was eventually confirmed to be the work of a pair of rogue males, who were believed to be responsible for as many as 140 deaths. Railway records officially attribute only 28 worker deaths to the lions, but the predators were also reported to have killed a significant number of local people of which no official record was ever kept, which attributed to the railway's smaller record.
