Benefitting from the flexibility in engineering the geometries of their artificial atoms and correspondingly the effective electromagnetic properties, metamaterials provide a unique platform for investigating the topological properties of photons. During the past few years, various topological photonic phases have been demonstrated with metamaterials, such as Weyl degeneracies, Dirac points and 3D topological insulators. Dirac point is a four-fold band crossing defined in 3D momentum space, away from which energy band exhibits linear dispersion along arbitrary directions. As a central gapless topological phase, Dirac semimetals bridge conventional insulators, topological insulators and Weyl semimetals. In this talk I will discuss how to use metamaterials to realize Dirac points in a four-band system by leveraging both electric and magnetic bulk plasmons. I will further show that the Dirac points can be promoted to Yang monopoles in a suitably chosen 5D synthetic space. The Yang monopoles can be transformed into linked Weyl surfaces by introducing certain perturbations to the system. An important signature of the second order nontrivial topology - the presence of 1D Weyl arcs and 3D Fermi hypersurfaces at the 4D boundary of the 5D system, will be described.