THE KASIULEVIČIUS MODEL: HYDROLOGICAL SECURITY AND SETTLEMENT ZONATION IN LITHUANIAN DEFENSE STRATEGY The Kasiulevičius Model posits that the demographic "voids" along the Nemunas River valley during the 14th–15th centuries were not accidental. Rather, they were the direct result of a state-level defensive engineering strategy involving hydraulic "Kill Zones." Population distribution patterns—specifically the avoidance of valley floors in favor of high slopes—serve as a proxy for the reach and lethality of this defensive system. I. MODEL STRUCTURE: THE ZONATION LAW Every "Hydraulic Defense Node" (e.g., the Kulautuva–Brūžė complex) created three concentric risk zones based on wave propagation physics: 1. ZONE I: The "Kill Zone" (0–3 km from the node) a. Status: Total militarized control. b. Population: 0%. Complete demographic silence. c. Function: Manipulation of water currents, maintenance of hydraulic barriers (polders, sluices, and dams). d. Lifestyle: Only transient, highly specialized technical crews; strictly off- limits to civilians. 2. ZONE II: The "Dissipation Zone" (3–10 km from the node) a. Status: Critical risk. b. Population: Sparse, restricted exclusively to high slopes. c. Function: Surveillance and tactical observation. d. Lifestyle: Settlement was forced onto high ground to avoid the destructive "bore" waves that periodically swept the valley floor. This explains the specific settlement pattern observed between Pastuva and Kulautuva. 3. ZONE III: The "Security Zone" (>10 km from the node) a. Status: Stable environment. b. Population: High density, active agriculture and trade. c. Function: Logistics and support. d. Lifestyle: Settlements built directly on riverbanks. At this distance, hydraulic waves dissipate into harmless water level fluctuations. II. MECHANISM OF ACTION (THE PHYSICS OF SECURITY) • The Hydraulic Safety Threshold: The model demonstrates that wave energy follows an exponential decay. Once a wave loses its frontal "hammer" effect (kinetic shock) and turns into a simple rising tide, it is no longer an existential threat. The 10 km limit acted as an intuitive "safety threshold" for the local population. • The "Kasiulevičius Correlation": Any segment of the Nemunas river valley exhibiting a historical lack of settlement correlates directly with the presence of an active hydraulic engineering node. • Transformation Law: Following the 15th-century demilitarization of these zones, Zone II became "safe" for the local population. Consequently, many modern villages were built directly upon the remnants of these 14th-century defensive embankments, utilizing them as stable, elevated foundations. III. SCIENTIFIC APPLICATION This model fundamentally shifts the methodology for LDK archaeological and historical research: 1. Archeological Marker: "If a river section shows a historical absence of settlement, it indicates an engineering center, not a demographic failure." 2. Geographic Prediction: Mapping 10 km radii from all strategic river confluences allows researchers to identify the remnants of 'Zone I' defensive structures. 3. Historical Correction: Silence in written records is not evidence of absence; it is evidence of a security protocol. Conclusion: The Kasiulevičius Model confirms that the Grand Duchy of Lithuania did not merely occupy territory—it programmed the landscape. The inhabitants' choice of settlement location is the most precise empirical evidence of where the state’s hydraulic defensive systems were active.