Psalms 55:10

Day and night they go about it, upon the walls thereof
That is, "violence" and "strife" go about the walls of it continually; men of violence and contention are the only watchmen of it: a city must be sadly guarded that has no better watch than this;

mischief also and sorrow [are] in the midst of it;
it was full of wickedness within and without; the city, as Aben Ezra observes, was like a circle; violence and strife were as a line round about it, and mischief and sorrow the centre of it: and these two commonly go together; where mischief is, sorrow follows.