We report angle-resolved photoemission (ARPES) measurements, density functional and model tight-binding calculations on Ba2IrO4 (Ba-214), an antiferromagnetic (T-N = 230 K) insulator. Ba-214 does not exhibit the rotational distortion of the IrO6 octahedra that is present in its sister compound Sr2IrO4 (Sr-214), and is therefore an attractive reference material to study the electronic structure of layered iridates. We find that the band structures of Ba-214 and Sr214 are qualitatively similar, hinting at the predominant role of the spin-orbit interaction in these materials. Temperature-dependent ARPES data show that the energy gap persists well above TN, and favor a Mott over a Slater scenario for this compound.