Portland cement
There then followed a number of independently discovered or copied versions of this "Portland cement" (also referred to as proto-Portland cement). Proto-Portland cement had a different chemical makeup from other natural cements being produced at the same time: It was burnt at a higher temperature than other Natural cements and thus crosses the barrier between traditional vertical kiln fired natural cement and the later horizontal kiln fired artificial cements. This cement is not, however, the same as the modern ordinary Portland cement, which can be defined as artificial cement.