# Architecture I: Structure and What It Permits

Art History I · Artistic Languages · https://tryals.app/learn/art-history-i/architecture-i-structure-and-what-it-permits

## The Problem Is Always the Span

Every building must hold a load and carry it to the ground. The structural system decides what spaces are possible.

| System | How it works | Limit | Characteristic space |
|---|---|---|---|
| **Post and lintel** | A beam across two supports | The beam's resistance to bending | Forest of columns, modest spans |
| **Corbelling** | Courses stepped inward | Very limited | Small chambers, false domes |
| **Arch** | Compression carried along a curve | Needs buttressing against outward thrust | Long spans, arcades |
| **Vault** | An arch extended or crossed | The same thrust, along a whole wall | Continuous covered space |
| **Dome** | An arch rotated | Thrust in every direction at the base | Great centralised interiors |
| **Frame** | A skeleton carries the load | Very few | Open plans, glass walls |

**Post and lintel** is the Greek system. Stone is strong in compression but weak in tension. A stone lintel fails by bending, so columns must sit close together.

**The arch** turns the load into compression along a curve. The price is **thrust**. An arch pushes outward as well as down, so buttresses or thick walls must resist it.

### Vaults, Domes, and Frames

**The vault** extends an arch in depth or crosses two arches.

**Gothic** architecture combines three key structural inventions:
- The **ribbed vault**
- The **pointed arches**
- The **flying buttress**

Together, these concentrate loads into specific points. The wall stops being structural, allowing vast expanses of stained glass.

**The dome** rotates an arch. Its thrust acts all around the base. Byzantine builders placed round domes over square plans using **pendentives**.

**The frame** uses iron, steel, or reinforced concrete. A skeleton carries the load, turning exterior walls into lightweight screens.

### Vitruvius

**Vitruvius** demanded three qualities in a building: *firmitas*, *utilitas*, and *venustas*. The structure settles its *firmitas* (solidity).

> **Common pitfall:** treating structure as mere engineering separate from style. The style is what the structure looks like when working.

## Practice questions

8 of this lesson's 13 practice questions, with answers. The full set is in the app.

### 1. Sort each feature by the structural system it belongs to.

**Answer:**

- Post and lintel: Dense, short spans, Stone beam in bending
- Arch and vault: Thrust needing butts, Continuous vault load
- Frame: Non-load curtain wall, Freely placed walls

**Why:** Each column is a different answer to the same question, and each answer produces its own kind of space: many short spans, long spans with heavy support, or an open plan with the wall reduced to a screen.

Page: https://tryals.app/practice/art-history-i/architecture-i-structure-and-what-it-permits/sort-each-feature-by-the-structural-system-it-belongs-to

### 2. The stained glass of a Gothic church is a consequence of its structural system rather than an addition to it.

**Answer:** True

**Why:** **True.** The ribbed vault and pointed arch concentrate thrust at points, and the flying buttress carries it out over the aisle. Once the wall no longer holds the building up, it can be opened, and the glass is what fills the space the structure released.

Page: https://tryals.app/practice/art-history-i/architecture-i-structure-and-what-it-permits/the-stained-glass-of-a-gothic-church-is-a-consequence-of-its

### 3. Stone is far stronger in compression than in tension. Roughly how many times stronger, as an order of magnitude?

**Answer:** 10 (within ±5)

**Why:** On the order of **ten times**, varying by stone. That single ratio explains the Greek temple: a stone lintel is loaded in bending, which puts its underside in tension, so it fails at a modest span, and the columns must therefore be close together.

Page: https://tryals.app/practice/art-history-i/architecture-i-structure-and-what-it-permits/stone-is-far-stronger-in-compression-than-in-tension-roughly-how

### 4. How many requirements did Vitruvius place on a building?

**Answer:** 3

**Why:** **Three**: *firmitas*, *utilitas*, *venustas*, it must stand up, be useful and please. Two thousand years later the list still works, and the structural system is where the first is settled.

Page: https://tryals.app/practice/art-history-i/architecture-i-structure-and-what-it-permits/how-many-requirements-did-vitruvius-place-on-a-building

### 5. An arch can bridge far wider gaps than a flat stone lintel because of how each handles forces. Why does this structural difference force the arch to generate outward thrust while the lintel does not?

A. Stone compresses only when curved, creating horizontal pressure at bases
B. Curved masonry requires continuous mechanical tension to avoid snapping
C. The lintel avoids all internal tensile stresses by resting horizontally
D. A curved geometry diverts downward gravity into lateral vector forces

**Answer:** D. A curved geometry diverts downward gravity into lateral vector forces

**Why:** Stone's weakness in tension limits flat spans where bending pulls the bottom face apart. Turning the span into an arch resolves downward weight purely into compressive forces along the curve, which necessarily push outwards at the springings.

Page: https://tryals.app/practice/art-history-i/architecture-i-structure-and-what-it-permits/an-arch-can-bridge-far-wider-gaps-than-a-flat-stone-lintel-because-of

### 6. Complete the account of structure.

**Answer:** Stone is strong in compression and weak in **tension**, which is why a stone lintel spans only a short distance. An arch converts the load into compression along a curve at the cost of outward **thrust**. The curved triangles that set a round dome on a square plan are **pendentives**. Once a **frame** carries the load, the wall becomes a screen.

**Why:** The four blanks are the whole causal chain of the lesson: a property of the material, a device that works around it, a device that works around that device's cost, and finally a material combination that dissolves the original constraint.

Page: https://tryals.app/practice/art-history-i/architecture-i-structure-and-what-it-permits/complete-the-account-of-structure

### 7. Arrange these structural systems in the order they became available in Western building.

**Answer:**

1. Post and lintel in stone
2. The true arch and the barrel vault
3. The pendentive dome
4. The ribbed vault with flying buttresses
5. The iron and steel frame

**Why:** The sequence is cumulative rather than replacing: post and lintel is still used, and the arch never went away. What each addition changed was the range of possible spaces, which is why the architectural repertoire keeps growing.

Page: https://tryals.app/practice/art-history-i/architecture-i-structure-and-what-it-permits/arrange-these-structural-systems-in-the-order-they-became-available

### 8. Arrange these buildings by the structural problem each is famous for solving.

**Answer:**

1. A Greek temple: many short stone spans
2. The Pantheon: a concrete dome on a circular drum
3. Hagia Sophia: a dome on a square plan
4. A Gothic cathedral: thrust carried outward from a ribbed vault
5. An early steel-framed tower: load carried by a skeleton

**Why:** Each building in the sequence is a solved problem, and the solution is what the building looks like. That is the argument of the lesson in one list: the structure is not behind the architecture, it is the architecture seen from inside.

Page: https://tryals.app/practice/art-history-i/architecture-i-structure-and-what-it-permits/arrange-these-buildings-by-the-structural-problem-each-is-famous-for