How did ancient constitutionalism challenge royal absolutism in Europe?

Ancient constitutionalism challenged royal absolutism by appealing to a "fundamental law"—a collection of long-standing customs, feudal oaths, and historical charters—rather than the unchecked will of a monarch. By framing royal actions as "innovations" that disrupted this established order, critics argued that such exercises of power were illegal and illegitimate.1

In England, this ideology was central to Parliamentarian and Whig thought. Proponents argued that rights, such as those codified in the Magna Carta, predated the Stuart kings, thereby establishing a legal baseline that constrained the crown. Similarly, in France, the parlementaires used their power to register royal edicts to issue remonstrances, arguing that the king must respect traditional laws and the privileges of intermediate bodies to avoid despotism.12

Ultimately, ancient constitutionalism served as a vital, if sometimes historically idealized, mechanism to assert that no ruler is above the rule of law, laying early groundwork for modern constitutional governance.13