Why is benzene aromatic?
It meets the requirements of aromaticity.
The rules from Chemwiki:
1. A planar (or near planar) cycle of sp2 hybridized atoms, the p-orbitals of which are oriented parallel to each other. These overlapping p-orbitals generate an array of π-molecular orbitals.
2.These π-orbitals are occupied by 4n+2 electrons (where n is an integer or zero). This requirement is known as The Hückel Rule. All the aromatic compounds discussed above have 6 π-electrons (n=1).
This structure, although shown with 3 double bonds, actually allows electron flow throughout the entire ring via p orbitals. This is why it is sometimes shown with a circle or dashed lines. This flow of electrons makes the molecule very stable.