Fasces were a bundle of birch rods wrapped together with an axe into one bundle (they were held together with ribbon). They were carried by lictors behind a magistrate to show their power to punish through beating and through execution. They therefore represent strength. The binding together also represents unity. Since fascism likes to associate itself with national strength and unity, they chose a name derived from the fasces (I believe the word 'fasces' [this is actually the plural but the singular isn't used] comes from the latin word 'fas' which means something along the lines of 'it is ordained').