otivm/docs/economy/otivm_iv_cost_calibration_model.md

OTIVM-IV Cost Calibration Model — Roman Merchant Economy, c. 14 BCE

Prepared for: OTIVM-IV / CIVICVS Simulator
Date: 2026-05-03
Status: Calibrated historical-economic model, not a claim of exact reconstruction
Baseline good selected: Plain ceramic cup / small clay vessel
Currency convention: 1 denarius (dn) = 16 asses (as)

---

1. Method

This document treats Roman economic evidence as a calibration field rather than as a complete price list. Values are divided into three categories:

• Source-backed anchors: values directly attested or strongly reported in ancient evidence or modern synthesis.
• Analogical conversions: values inferred from better-attested wages, food prices, transport charges, or later Roman price schedules.
• Simulator calibrations: values required for balanced equations where no direct evidence survives.

The objective is not exactness. The objective is defensibility, internal consistency, and clean decomposition into named constants.

Confidence labels

Label	Meaning
HIGH	Directly attested or widely accepted anchor; suitable as a calibration base.
MEDIUM	Inferred from adjacent evidence, but historically plausible and equation-safe.
LOW	Needed by the model but not directly recoverable; treat as calibration.

---

2. Currency and Equation Rules

Currency

• 1 dn = 16 as
• All simulator costs should resolve to denarii internally.
• UI may show small daily or per-item prices in asses where that better reflects ancient small-denomination accounting.

Conversion

dn = as / 16
as = dn * 16

Otium-cycle convention

The mockup uses an existing placeholder of −8 dn for the next otium cost. This model preserves that magnitude because it is plausible for a cycle covering roughly one to two weeks of a middling merchant’s subsistence and social operating costs.

Recommended equation:

otium_cycle_cost =
    otium_access_fee
  + personal_maintenance
  + officia_obligation

Recommended simulator constants:

OTIUM_ACCESS_FEE_DN        = 2.00
PERSONAL_MAINTENANCE_DN   = 4.00
OFFICIA_OBLIGATION_DN     = 2.00
OTIUM_CYCLE_TOTAL_DN      = 8.00

These should remain separately logged in parameter_drift_log.

---

3. Reference Wages and Price Anchors

These anchors should calibrate all derived constants.

Reference item	Amount	Period / unit	Source	Confidence	Notes
Legionary soldier, miles gregarius, Augustan stipendium	225 dn	annual gross pay	Augustus-era army-pay tradition; modern syntheses commonly give 225 denarii/year for the Augustan legionary.	HIGH	Best first-century monetary anchor. Deductions for rations/equipment complicate net disposable pay.
Legionary soldier, implied daily gross	0.616 dn = 9.86 as	per day	Derived from 225 dn / 365 days.	HIGH	Use only as gross annualized pay, not as free cash.
Unskilled day laborer	0.375–0.625 dn = 6–10 as	day	Calibrated from Roman Egypt wage studies and later Diocletianic wage schedules.	MEDIUM	Direct Augustan Italian data are thin. Use 0.50 dn/day as simulator midpoint.
Skilled artisan / craft worker	0.75–1.25 dn = 12–20 as	day	Calibrated from later craft wages and relative skill premium; terracotta figurine maker in the Diocletianic Edict is listed above common labor.	MEDIUM	Use 1.00 dn/day as simulator midpoint for potter/craft labor.
Potter / terracotta specialist	1.00 dn	day	Analogical: Diocletianic wage schedule lists maker of terracotta figurines at a higher daily rate than common labor.	MEDIUM	For mass pottery, per-item labor is tiny because production is batched.
Elementary teacher	Analogical only	monthly per pupil	Diocletianic Edict lists elementary teacher monthly per pupil; later, not Augustan.	LOW	Use as relative status anchor, not as direct Augustan Italian price.
Teacher of Greek/Latin literature / geometry	Analogical only	monthly per pupil	Diocletianic Edict lists literature/geometry teacher above elementary teacher.	LOW	Can anchor literacy/status costs if education mechanics are later added.
Roman magistrate public salary	0 dn	annual public salary	Republican/early imperial civic magistracies were generally honorific and unpaid; office could impose private expense.	HIGH	Useful negative anchor: status office creates obligation more than salary.
Modius of wheat	0.50–1.00 dn = 8–16 as	per modius	Calibrated from early imperial grain-price discussions and later food-price schedules.	MEDIUM	Use 0.75 dn/modius as simulator food-cost midpoint for central Italy.
One adult grain need	4–5 modii/month	monthly	Standard ancient subsistence approximation.	MEDIUM	Implies grain cost alone of roughly 3–4 dn/month at 0.75 dn/modius.
Personal bare food floor	0.12–0.20 dn	day	Derived from wheat consumption plus simple additions.	MEDIUM	Merchant maintenance must be higher than this due to lodging, clothing, harbor expenses.
Road freight, full wagon	Later analogical	per mile	Diocletianic Edict preserves road transport charges by wagon/load.	LOW	Use for ratios only; not direct Augustan prices.
Sea freight	Later analogical	per route / volume	Diocletianic Edict preserves sea freight by route and volume.	LOW	Useful for relative route cost, not exact first-century amount.

Recommended wage constants

WAGE_UNSKILLED_DAY_DN     = 0.50
WAGE_SKILLED_ARTISAN_DN   = 1.00
WAGE_MERCHANT_SELF_DN     = 1.00
WHEAT_MODIUS_DN           = 0.75

---

4. Table 1 — Periodic Operating Costs

Cost item	Amount (dn)	Per cycle	Source	Confidence	Notes
OTIVM access / commercial information retainer	2.00 dn	per otium cycle	Calibration from commercial association, factor, broker, and information-access behavior; no exact “subscription” equivalent is known.	LOW	Represents letters, informants, harbor gossip, factor access, and maintaining a place in commercial knowledge channels.
Personal maintenance	4.00 dn	per otium cycle	Derived from wheat-price anchor, lodging, simple meals, clothing upkeep, lamps/oil, local movement.	MEDIUM	Plausible for a middling working merchant over roughly 7–14 days; above subsistence, below elite consumption.
Officia obligations	2.00 dn	per otium cycle	Calibration from Roman patronage, collegial obligations, tips, gifts, unrepaid favors, and small social expenses.	LOW	Should fluctuate by status and events. Baseline represents ordinary soft obligations, not crisis bribes.
Total recommended otium cycle cost	8.00 dn	per otium cycle	Sum of three components.	MEDIUM	Preserves mockup magnitude while decomposing it into citable triggers.

Periodic-cost equation

otium_cycle_cost_dn =
    2.00  // otium_access_fee_dn
  + 4.00  // personal_maintenance_dn
  + 2.00  // officia_obligation_dn
= 8.00 dn

Drift-log mapping

Cost item	Suggested trigger_type	Parameter affected
OTIVM access	otium_access_fee	liquiditas, possibly mercatus_scientia maintenance
Personal maintenance	personal_maintenance	liquiditas
Officia obligations	officia_obligation	liquiditas, clientela, fama

---

5. Baseline Goods Model Selection

The originally proposed wicker basket is useful, but ceramic vessels are a stronger first baseline because Roman pottery is archaeologically abundant, batched, transportable, breakable, and well suited to equation decomposition.

Candidate	Decision	Reason
Plain ceramic cup / small clay vessel	SELECTED	Best balance of archaeological richness, simple material flow, batch production, and transport/market logic.
Wicker basket	Defer	Good for seasonal organic material, but direct price evidence is weaker.
Axe	Defer	Strong labor/material model, but iron pricing and smithing variability complicate first baseline.
Army tent	Defer	Useful later for military supply; textile/leather input model is more complex.
Chair/table	Defer	Too variable by wood species, joinery, finish, and status market.

---

6. Table 2 — Plain Ceramic Cup / Small Clay Vessel Full Cost Structure

Baseline assumptions

• Product: plain local ceramic cup or small cup-like vessel.
• Production mode: batched workshop production.
• Sale context: town or harbor market in Roman Italy.
• Finished item simulator retail value: 2 as = 0.125 dn.
• Fine/slipped or branded version may be doubled to 4 as = 0.25 dn.
• This is deliberately a humble good; the value comes from repeatable structure, not high margin.

Cost components

Component	Amount (dn or as)	Source	Confidence	Notes
Clay extraction / raw clay	0.125 as = 0.0078 dn	Calibration from low raw-material value; clay is local and low cost.	LOW	Clay is abundant; cost is mainly labor/access, not material scarcity.
Water and preparation	0.125 as = 0.0078 dn	Calibration from workshop preparation logic.	LOW	Includes levigation, kneading, and waste loss at tiny per-unit batch share.
Permit/customary access fee for clay pit	0.125 as = 0.0078 dn	Calibration from estate/public-land access logic.	LOW	No direct cup-level fee; included so the supply-chain equation has an access-cost slot.
Transport of raw clay to workshop	0.25 as = 0.0156 dn	Calibration from short local haul; later transport schedules only support relative scale.	LOW	Should be near zero if workshop sits near clay source; increase for urban workshops.
Potter labor	0.50 as = 0.03125 dn	Derived from skilled wage 1 dn/day and batch production.	MEDIUM	Assumes one potter can form many simple vessels per day; labor share is small per cup.
Assistant / unskilled labor	0.125 as = 0.0078 dn	Derived from 0.50 dn/day unskilled wage and batch support.	MEDIUM	Includes moving clay, stacking, cleaning, carrying.
Kiln fuel	0.25 as = 0.0156 dn	Calibration from kiln batch fuel spread across many items.	LOW	Fuel matters at workshop scale but is small per cup if firing is efficient and batched.
Kiln depreciation / tools	0.125 as = 0.0078 dn	Calibration.	LOW	Covers wheel, tools, kiln wear, wasters.
Workshop overhead	0.25 as = 0.0156 dn	Calibration from rent, storage, supervision, breakage.	LOW	Needed for equation completeness.
Breakage / waster allowance	0.125 as = 0.0078 dn	Archaeological pottery studies emphasize breakage, discard, and lifecycle effects.	MEDIUM	Small per-unit surcharge; should rise for long-distance trade.
Finished-goods transport to local market	0.25 as = 0.0156 dn	Calibration from short haul.	LOW	If carried to stall locally, this is small. For intercity transport, route system should add separate vectura.
Portoria / toll	0 as local; 0.125 as if crossing toll boundary	Portoria commonly modeled as low ad valorem toll; use only when route crosses toll district.	MEDIUM	For local sale, zero. For transported goods, use route-level toll rather than baked-in cost.
Market fee / stall share	0.25 as = 0.0156 dn	Calibration from market-control/stall logic.	LOW	Represents daily stall rent or market dues allocated per item.
Merchant margin	0.50 as = 0.03125 dn	Calibration.	MEDIUM	Needed to make the item worth handling; roughly 25% of final retail price.
Total local retail price	2.00 as = 0.125 dn	Sum of components.	MEDIUM	Equation-safe humble ceramic cup baseline.

Baseline ceramic-cup equation

ceramic_cup_local_cost_as =
    clay_raw_as
  + clay_prep_as
  + clay_access_fee_as
  + raw_transport_as
  + potter_labor_as
  + assistant_labor_as
  + kiln_fuel_as
  + kiln_depreciation_as
  + workshop_overhead_as
  + breakage_allowance_as
  + finished_transport_as
  + local_portoria_as
  + market_fee_as
  + merchant_margin_as

With recommended values:

ceramic_cup_local_cost_as =
    0.125
  + 0.125
  + 0.125
  + 0.250
  + 0.500
  + 0.125
  + 0.250
  + 0.125
  + 0.250
  + 0.125
  + 0.250
  + 0.000
  + 0.250
  + 0.500
= 3.000 as

This sum is too high for the chosen 2 as retail target. Therefore the first naive component allocation overstates the unit burden. Batch production must compress overhead and labor further.

Corrected baseline equation

For the simulator, use a 2-as local cup and group micro-costs into batch categories:

Aggregated component	Amount	Notes
Raw material and preparation	0.25 as	Clay, water, preparation, access.
Workshop labor	0.50 as	Potter and assistant batch share.
Kiln/fuel/tools	0.375 as	Firing and tool wear.
Breakage allowance	0.125 as	Wasters and handling loss.
Local transport and market fee	0.25 as	Stall and short transport.
Merchant margin	0.50 as	Incentive to handle and sell.
Total	2.00 as = 0.125 dn	Recommended base constant.

Corrected equation

ceramic_cup_base_as =
    raw_material_prep_as      // 0.25
  + workshop_labor_as         // 0.50
  + kiln_fuel_tools_as        // 0.375
  + breakage_allowance_as     // 0.125
  + local_transport_market_as // 0.25
  + merchant_margin_as        // 0.50
= 2.00 as

Variant constants

Good constant	Amount	Use
CERAMIC_CUP_PLAIN_LOCAL_AS	2 as	Local plain vessel.
CERAMIC_CUP_FINE_LOCAL_AS	4 as	Better finish, slip, stamp, or preferred workshop.
CERAMIC_CUP_TRANSPORTED_AS	3 as	Plain vessel after intercity transport and toll burden.
CERAMIC_CUP_BREAKAGE_RATE_LOCAL	0.05	Local handling.
CERAMIC_CUP_BREAKAGE_RATE_INTERCITY	0.12	Longer transport.
CERAMIC_CUP_PORTORIA_RATE	0.025	Use 2.5% ad valorem where toll applies.

---

7. Simulator Constants

Currency

AS_PER_DENARIUS = 16

Wages

WAGE_UNSKILLED_DAY_DN     = 0.50
WAGE_SKILLED_ARTISAN_DN   = 1.00
WAGE_MERCHANT_SELF_DN     = 1.00
WAGE_LEGIONARY_YEAR_DN    = 225.00

Food and maintenance

WHEAT_MODIUS_DN             = 0.75
MERCHANT_DAILY_MAINT_DN     = 0.35
OTIUM_CYCLE_DAYS            = 10
PERSONAL_MAINTENANCE_DN     = 4.00

Note: MERCHANT_DAILY_MAINT_DN * 10 = 3.50 dn; rounded to 4.00 dn to include incidental urban expense.

Otium

OTIUM_ACCESS_FEE_DN        = 2.00
OFFICIA_OBLIGATION_DN      = 2.00
OTIUM_CYCLE_TOTAL_DN       = 8.00

Ceramic baseline

CERAMIC_CUP_PLAIN_LOCAL_AS       = 2.00
CERAMIC_CUP_FINE_LOCAL_AS        = 4.00
CERAMIC_CUP_TRANSPORTED_AS       = 3.00
CERAMIC_CUP_PORTORIA_RATE        = 0.025
CERAMIC_CUP_BREAKAGE_LOCAL_RATE  = 0.05
CERAMIC_CUP_BREAKAGE_ROUTE_RATE  = 0.12

Route toll

PORTORIA_AD_VALOREM_RATE_LOW     = 0.025
PORTORIA_AD_VALOREM_RATE_HIGH    = 0.050

Use 0.025 as default.

---

8. Confidence Register

Model value	Confidence	Reason
225 dn Augustan legionary stipend	HIGH	Strong standard anchor.
1 dn = 16 as	HIGH	Stable Roman accounting convention after denarius retariffing.
Magistracy as unpaid / expense-bearing	HIGH	Good civic-status rule.
0.50 dn unskilled daily wage	MEDIUM	Plausible synthesis; not exact 14 BCE Italy.
1.00 dn skilled artisan daily wage	MEDIUM	Relative skill premium supported by later schedules.
0.75 dn per modius wheat	MEDIUM	Plausible central-Italy simulation midpoint.
8 dn otium cycle	MEDIUM	Defensible if cycle means about 10 days of middling maintenance plus social costs.
2 dn OTIVM access	LOW	Direct equivalent does not exist; calibration for information access.
2 dn officia	LOW	Historically real category, weakly priceable.
2 as plain ceramic cup	MEDIUM	Plausible low-value mass good; exact Augustan price not directly attested here.
Ceramic component breakdown	LOW–MEDIUM	Equation-safe allocation, not direct ancient accounting.

---

9. Open Questions / Calibration Flags

1. Otium cycle length
   The equations become clearer if the game formally defines one otium cycle as 10 sim days. If the intended cycle is shorter or longer, PERSONAL_MAINTENANCE_DN should scale with days while OTIUM_ACCESS_FEE_DN and OFFICIA_OBLIGATION_DN may remain fixed or semi-fixed.

2. OTIVM subscription category
   No direct Roman “subscription to trade intelligence” price should be expected. Treat as a composite of factor access, letters, informants, harbor networks, and collegial standing.

3. Officia
   This should become event-sensitive. Suggested multiplier:

   officia_cost = base_officia * status_multiplier * event_pressure
   

   Where status_multiplier rises with auctoritas and clientela.

4. Pottery transport
   The local cup is useful as a production baseline but not as a lucrative trade good. Transported ceramics should be modeled in batches, not as single-item cargo.

5. Fine ware
   Terra sigillata or stamped fine ware should be a separate product class. It is not merely a plain cup with higher price; it implies different production organization, reputation, and distribution.

---

10. Bibliography and Evidence Notes

Primary / ancient evidence

• Diocletian, Edictum de Pretiis Rerum Venalium, AD 301. Used only as a later Roman relative price and wage schedule, not as direct 14 BCE pricing.
• Polybius, Histories, Book 6. Used for Republican military pay/ration context.
• Suetonius / Augustus-era military-pay tradition. Used indirectly through modern synthesis for Augustan stipendium.

Modern works and datasets consulted

• Antony Kropff, An English translation of the Edict on Maximum Prices, also known as the Price Edict of Diocletian, version 2.1, 2016.
  URL: https://kark.uib.no/antikk/dias/priceedict.pdf

• Walter Scheidel, Real wages in Roman Egypt: A contribution to recent work on pre-modern living standards, Princeton/Stanford Working Papers in Classics, 2008.
  URL: https://www.ancientportsantiques.com/wp-content/uploads/Documents/AUTHORS/Scheidel2008-Wages.pdf

• J. Theodore Peña, Roman Pottery in the Archaeological Record, Cambridge University Press, 2007.
  Used for pottery lifecycle framing: manufacture, distribution, use, reuse, maintenance, recycling, discard, reclamation.

• Heli Kiiskinen, Production and Trade of Etrurian Terra Sigillata Pottery in Roman Etruria and beyond between c. 50 BCE and c. 150 CE, 2013.
  Used for transport/distribution relevance of Italian terra sigillata and the caution that pottery trade involved multiple models.

• Richard Duncan-Jones, The Economy of the Roman Empire: Quantitative Studies, 2nd ed., Cambridge University Press, 1982.
  General calibration background for prices, costs, and quantitative Roman-economy evidence.

• Peter Temin, The Roman Market Economy, Princeton University Press, 2013.
  General market-context support.

• Walter Scheidel, Ian Morris, and Richard Saller, eds., The Cambridge Economic History of the Greco-Roman World, Cambridge University Press, 2007.
  General economic background and scale calibration.

• Jean Andreau, Banking and Business in the Roman World, Cambridge University Press, 1999.
  Used for commercial-network context.

• Koenraad Verboven, The Economy of Friends: Economic Aspects of Amicitia and Patronage in the Late Republic, Latomus, 2002.
  Used for officia, patronage, and social-economic obligations.

• Philip A. Harland, Associations, Synagogues, and Congregations, 2nd ed., 2013.
  Used for collegial and association behavior as social-economic context.

---

11. Implementation Note

Recommended database insertion pattern:

parameter_drift_log.trigger_type = 'otium_access_fee'
parameter_drift_log.delta_note   = 'Commercial information access and factor network maintenance.'
parameter_drift_log.value_after  = liquiditas_before - OTIUM_ACCESS_FEE_DN

parameter_drift_log.trigger_type = 'personal_maintenance'
parameter_drift_log.delta_note   = 'Food, lodging, clothing upkeep, light, and local movement.'
parameter_drift_log.value_after  = liquiditas_after_access - PERSONAL_MAINTENANCE_DN

parameter_drift_log.trigger_type = 'officia_obligation'
parameter_drift_log.delta_note   = 'Patronage, tips, gifts, collegial contributions, and unrecovered favors.'
parameter_drift_log.value_after  = liquiditas_after_maintenance - OFFICIA_OBLIGATION_DN

This preserves the current −8 dn design while making the ledger explainable and citable.