A true arch allows the building of very high and wide doorways. To form a true arch, stones are laid against each other in a semicircular pattern in such a way that load or weight of the entire structure is shifted to the ‘keystone’, a specially shaped stone at the apex (highest point) of the arch. Because of this offsetting pressure, the overall structure does not collapse due to its own excessive weight, as it would otherwise do. So, true arches allow much larger and more majestic-looking doorways than straight doors, which would need many, many pillars around the room to hold up the structure.
The first use of the True Arch in India is perhaps in the mausoleum of the last slave king Ghiyas-ud-din Balban in 1287. The Turks were familiar with the True Arch for much longer, in fact Emperor Septimius Severus rebuilt the provincial city of Byzantium in 203 CE and endowed it with a Hippodrome — a course for horse racing, I have seen a fully preserved True Arch in one of the walls of the Hippodrome and there will be more. The True Arch existed in Ephesus from at least the 1st century of the Common Era and at the capital city from 200 years earlier and the Turks could not have been unaware of the form.
Picture Credit : Google