Source of the doctrine of the separation of powers

The origins of the doctrine of the separation of powers are often traced to John Locke’s Second Treatise of Government (1689), in which he identified the 'Executive' and 'legislative' powers as needing to be separate.

‘…it may be too great a temptation to human frailty, apt to grasp at power, for the same persons, who have the power of making laws, to have also in their hands the power to execute them, whereby they may exempt themselves from obedience to the laws they make…’

Its classic exposition is however that of the Baron de Montesquieu, writing about the constitution of England in L’Esprit des Lois (1748), in which he identified judicial power as the third branch of government.

‘When the legislative and executive powers are united in the same person, or in the same body of magistrates, there can be no liberty; because apprehensions may arise, lest the same monarch or senate should enact tyrannical laws, to execute them in a tyrannical manner.

Again, there is no liberty,