Early in the 4th century (312 AD), the Roman Emperor Constantine made Christianity the legal religion of the Roman Empire. The Christians who had been worshipping secretly in private houses now wanted to build churches. They did not want the churches to look the same as Roman Temples. They built them to look more like Roman Basilicas. A basilica was a good plan for a Christian church because lots of people could fit inside, and the aisles were useful for people to move around. The semi-circular part at one end, the "apse", was just right to put the altar. Christian basilicas usually have the door at one end, rather than at the side. In front of the door there was often a courtyard called an "atrium". Most of these atriums have gone, but churches often have a town square or a market place in front of them.