 Mendelssohn 's mature symphonies are numbered approximately in the order that they were published , rather than the order in which they were composed . The order of actual composition is : 1 , 5 , 4 , 2 , 3 . The placement of No. 3 in this sequence is problematic because he worked on it for over a decade , starting sketches for it soon after beginning work on No. 5 , but completing it after both Nos. 5 and 4 . 
