Angle-Trisecting House System
The Porphyry house system, attributed to the 3rd-century Neoplatonist philosopher Porphyry, divides each of the four quadrants of the chart (defined by the Ascendant, IC, Descendant, and Midheaven) into three equal arcs. The four angles are fixed; the intermediate house cusps are calculated by trisecting the arc between them. It is simpler than Placidus and Koch, works at all latitudes without breakdown, and is respected for its historical pedigree as one of the first quadrant house systems.
Porphyry Characteristics
| Feature | Porphyry |
|---|---|
| Angles | Fixed (ASC, IC, DSC, MC) |
| Intermediate cusps | Trisection of each quadrant arc |
| House sizes | Unequal but uniform within each quadrant |
| Polar latitudes | Works — no breakdown |
| Historical period | 3rd century CE |
When to Use Porphyry
Porphyry is valued as a historically grounded alternative to Placidus for Hellenistic chart work, since it is an early quadrant system that preserves the four angular cusps. It is simpler and more geometrically consistent than Placidus, and because it does not break down at extreme latitudes, it is the preferred quadrant system for charts from Iceland, Alaska, Scandinavia, and other high-latitude locations. Traditional and Hellenistic practitioners working with quadrant houses often find Porphyry produces accurate and interpretable results.