Separation of powers
The separation of powers, often imprecisely used interchangeably with the trias politica principle, is a model for the governance
Governance is the act of governing. It relates to decisions that define expectations, grant power, or verify performance. It consists of either a separate process or part of management or leadership processes...

 of a state. The model was first developed in ancient Greece
Ancient Greece
Ancient Greece is a civilization belonging to a period of Greek history that lasted from the Archaic period of the 8th to 6th centuries BC to the end of antiquity. Immediately following this period was the beginning of the Early Middle Ages and the Byzantine era. Included in Ancient Greece is the...

 and came into widespread use by the Roman Republic
Roman Republic
The Roman Republic was the period of the ancient Roman civilization where the government operated as a republic. It began with the overthrow of the Roman monarchy, traditionally dated around 508 BC, and its replacement by a government headed by two consuls, elected annually by the citizens and...

 as part of the unmodified Constitution of the Roman Republic
Constitution of the Roman Republic
The Constitution of the Roman Republic was a set of guidelines and principles passed down mainly through precedent. The constitution was largely unwritten, uncodified, and constantly evolving...

. Under this model, the state
State (polity)
A state is an organized political community, living under a government. States may be sovereign and may enjoy a monopoly on the legal initiation of force and are not dependent on, or subject to any other power or state. Many states are federated states which participate in a federal union...

 is divided into branches, each with separate and independent powers and areas of responsibility so that no one branch has more power than the other branches.