In this task, you are given a question and a context passage. You have to answer the question based on the given passage.

What made travel scary to do at night time by main characters in novels?, Context: The Fujiwara rulers failed to maintain adequate police forces, which left robbers free to prey on travelers. This is implicitly illustrated in novels by the terror that night travel inspired in the main characters. The shōen system enabled the accumulation of wealth by an aristocratic elite; the economic surplus can be linked to the cultural developments of the Heian period and the "pursuit of arts". The major Buddhist temples in Heian-kyō and Nara also made use of the shōen. The establishment of branches rurally and integration of some Shinto shrines within these temple networks reflects a greater "organizational dynamism".
robbers free to prey on travelers