Solarae is a militaristic kingdom that has long guarded the northern passes against the hordemen (think the Germanic migrations/migrants), but Solarae is also a rich kingdom due to the abundance of metal both within the highlands, but also through trade with the dverg (think dwarves). Because of these factors Solarae faces both invasion by the hordes, but also it's fellow kingdoms jealous of its wealth (this animosity isn't helped by Solarae frequently being the "bully" of regional conflicts).
Long ago the "King of all Sol", Merovech the Stern created a system of corvee labor within his kingdom. The system is as follows:
For every 3 weeks the peasantry (serfs) are at their manors they must for one week labor for the crown. In order to have a constant flow of labor the serf population will be divided into roughly 4 groups with each having a different labor week within a given month. This means that 1/4 of the serfs would be laboring for the crown while the other 3/4 are at home.
The royal labor itself revolves around the building of fortifications or gathering the resources to build the fortifications. This means most serfs would be employed in quarries, or as wood cutters, brick layers, or other menial roles.
Would this system be effective or at least be moderately successful as "quickly" building or repairing fortifications and castles across solarae (as well as other building projects like roads, bridges, and so on)?
Late Medieval to Early Renaissance technology is in use.
Solarae itself is a abolitionist monarchy hence it's centralized nature.
The Kings of Solarae enforce their rule via the control of the mines and thus armor, weapon, and tool making of the kingdom as well as a small, but professional army of enforcers that beat lords who's heads get to big.
Solarae is in a near constant state of warfare dealing with invasions from the north and incursions by the other kingdoms from the south. However on the southern front it is minimal skirmishes at best.
The peasants are paid in rations, tools, and other necessities for their work.