progressive_fortifications

Progressive fortification is a multi-level constructed object that provides area-wide bonus to allied units. Example is a castle constructed in stages:
Stage 1: Fortification provides 10% damage reduction to units inside
Stage 2: Fortification provides 20% damage reduction to units inside
Stage 3: Fortification provides 30% damage reduction to units inside
Stage 4: Fortification provides 40% damage reduction to units inside
Stage 5: Fortification provides 50% damage reduction to units inside
Stage 6: Fortification provides 60% damage reduction to units inside
Stage 7: Fortification provides 70% damage reduction to units inside
Stage 8: Fortification provides 80% damage reduction to units inside
Stage 1: Fortification provides 90% damage reduction to units inside
Stage 10: Castle complete. 100% damage reduction(all damage is vs Castle, not units inside)
(Reduced damage goes to damage to castle HP,i.e. when 30% reduction: 30% reduced from castle HP(requiring repair) and 70% reduced from player HP)