Fortification is priced in person-days, and the pricing shows where to spend them: ringing a settlement of 150 m radius, a perimeter of 942 m, with a V-section ditch costs about 177 person-days, a dry-stone wall 785 to 1,047 waller-days, and a thorny hedge 4,187 to 6,280 plants and several years. A ditch crossing itself delays a walker by only seconds, so build barriers where they channel people into a watched gate or stop vehicles, not as a continuous ring.
Part of Defensive Architecture
Cost-benefit of fortification is the comparison of the labour a defensive feature takes against the time, warning or channelling it gives, so that effort goes where it protects most.
Labour Spent On Walls Is Labour Not Spent On Food
The defensive-architecture guide warns against fortifications that consume excessive labour: a castle takes years, and that labour is better spent on food production, water and community, which are also the real security. It names the ditch-and-berm, hedge, wall and palisade as the passive features. This article puts a number on each, using the household security guides’ figures (Ditches and Berms, Walls, Stone and Earth, Fences and Palisades, Thorny Hedgerows).
Worked Example: Pricing A Perimeter
Inputs: perimeter 2π × 150 = 942 m (an illustrative settlement radius); digging at 1 m³ per person-hour, the figure the perimeter guide gives; an 8-hour day; a V ditch 2 m wide and 1.5 m deep, cross-section ½ × 2 × 1.5 = 1.5 m²; a square-sided ditch of the same width and depth, 2 × 1.5 = 3 m², and 4 m² at 2 m deep (the defensive-architecture guide’s 1.5-2 m deep, 2 m wide); a dry-stone wall 1.5 m³ of stone per metre, built at 0.9-1.2 m a day per skilled waller; a hedge in a staggered double row with plants 30-45 cm apart.
- V ditch: 1.5 × 942 = 1,413 m³; at 1 m³ per hour 1,413 hours; ÷ 8 = 177 person-days.
- Square-sided ditch 3 m²: 2,826 m³, 353 person-days. At 4 m²: 3,768 m³, 471 person-days.
- Dry-stone wall: 942 ÷ 1.2 = 785 to 942 ÷ 0.9 = 1,047 waller-days, before gathering and hauling 942 × 1.5 = 1,413 m³ of stone.
- Palisade of 20 cm logs: 5 logs a metre, 942 × 5 = 4,710 logs; timber per 50 m is about 20 m³, so 942 ÷ 50 × 20 = 377 m³. The trench is small, 0.15 m³ per metre or 141 m³, but felling and hauling the logs is the heavy part.
- Hedge: two rows, 942 ÷ 0.45 = 2,093 to 942 ÷ 0.30 = 3,140 plants a row, so 4,187 to 6,280, and 2-5 years before it stops a person.
- Per adult, if 100 adults share it: V ditch 177 ÷ 100 = 1.8 days; wall 7.9-10.5 days. For comparison, the maintenance rota needs 8-12 days per adult a year (Community Maintenance Rotation).
What a crossing is worth. Suppose a walker crosses a ditch and berm 3.5 m wide at 0.5 m/s instead of walking at 1.4 m/s (both assumed). Time 3.5 ÷ 0.5 = 7 s against 3.5 ÷ 1.4 = 2.5 s: a delay of 4.5 s. A plank removes most of that. The value of a ditch is elsewhere: it stops vehicles and animals, and with gaps it forces people to a watched gate. With three gates equally spaced round 942 m, a walker at a random point is on average 942 ÷ 3 ÷ 4 = 78.5 m from the nearest gate and at most 157 m, which is 56 to 112 s of walking at 1.4 m/s, all of it in view.
What You Need
- Labour figures for your own people, measured by a trial section
- The approach map, with the routes ranked
- A decision on which layers to build where (Layers of Defense Concept)
- Lookouts and dogs, which cost almost nothing against the figures above
Method: Spend Where It Counts
Step 1: Price the options as above, for the lengths you actually need.
Step 2: Rank the approaches and defend the top two or three, not the whole ring. Three approaches of 100 m each with a V ditch is 300 × 1.5 = 450 m³, 56 person-days.
Step 3: Plant the hedge now if one is wanted, because its delay is the longest.
Step 4: Put the stone wall only where the approach is narrow.
Step 5: Put the gate under two lookouts and make the barrier lead to it.
Step 6: Review after a season against the food and water work that was delayed.
Common Mistakes
- A continuous ring. It costs the most and delays the least.
- A barrier nobody watches. An unobserved ditch can be bridged in minutes.
- Counting only the digging. Gathering stone and felling logs cost more than the trench.
- Forgetting the upkeep. Ditches silt and hedges need laying and trimming.
Safety
Trenches collapse and stakes kill the wrong people
A ditch 1.5 m deep is deep enough for a collapse to bury a person: slope the sides, never undercut the face and never dig alone. Do not put sharpened stakes in a ditch; a child, a lamb or one of your own in the dark is as likely to fall in as an intruder. Fence or mark ditches near children, and keep gaps and emergency openings for your own people (Ditches, Berms & Earthworks).
What’s Next
- Learn next: Hardened Structures — the inner layer
- Combine with: Passive Defensive Features — what the labour buys