What does breaking of sigma bonds need more energy than pi bonds?

@ sachet 
during the formation of sigma bond . overlap of atomic orbital takes place to a larger extent , whereas during the formation of pi bond , the overlapping of atomic orbital take place to a smaller extent . 
more the extent of overlapping ,, more the strength of bonds . 
therefore sigma bond is more stronger than pi bond , 
and obviously the more stronger bond reuqires more energy to break down . 
so, due to that sigma bond requires more energy 
HOPE IT CLEARS YOUR DOUBT 

ALL THE BEST ..

in a sigma bond electron density is spread symmetrically ,cylindrically around inter nuclear axis. hence sigma bond is strong.