In the famous monument Hagia Sophia, the central dome is mainly supported by which architectural feature?

Introduction / Context:
This question belongs to world art and architectural history, which is often included within wider world geography and culture sections. Hagia Sophia in Istanbul is one of the most important historic buildings in the world, originally built as a Byzantine church and later used as a mosque and now a museum or mosque complex. Its huge central dome is an engineering and artistic landmark. The question tests your knowledge of the structural system that supports this dome.

Given Data / Assumptions:

• The building in question is Hagia Sophia, located in Istanbul, Turkey.
• The focus is on the structural support of its central dome.
• Options include pendentives, flying buttresses, timber trusses, and corbelled squinches.
• We assume the classical description from architectural history that explains how the dome transitions from a square base to a circular shell.

Concept / Approach:
Hagia Sophia is famous for using pendentives, which are curved triangular sections that transition from a square or rectangular base to support a circular dome. These pendentives rest on four massive piers at the corners of the main square space. The system allows the weight of the dome to be channelled down through the piers and into the foundations. While later buildings such as Gothic cathedrals extensively used flying buttresses, Hagia Sophia itself relies primarily on pendentives and internal supports for the dome.

Step-by-Step Solution:
Step 1: Visualise the interior of Hagia Sophia. There is a huge central dome over a roughly square main space, with semi domes and galleries around. Step 2: Recall that the main structural innovation of Hagia Sophia was the use of pendentives, which are triangular curved surfaces filling the corners between arches. Step 3: Understand that these pendentives allow a round dome to sit above a square plan by gradually transferring the load from the dome to four supporting arches and piers. Step 4: Compare the options. Flying buttresses are external supports typical of Gothic cathedrals, not the primary support for Hagia Sophia's dome. Step 5: Timber truss systems and corbelled squinches do not describe the main system used here, so the correct choice is the pendentive system resting on four piers.

Verification / Alternative check:
Art and architecture textbooks often emphasise that Hagia Sophia marks a key stage in the development of Byzantine dome construction through pendentives. Diagrams show a square base, four arches, and curved triangular areas between them, which are the pendentives. These images and explanations make it clear that pendentives are the major element supporting the dome, while other features such as buttresses play secondary roles or are not characteristic of this specific structure.

Why Other Options Are Wrong:
Option B, a ring of flying buttresses, describes a visible feature of many Gothic cathedrals in western Europe but is not the primary device in Hagia Sophia. Option C, a timber truss roof, would be typical of many simpler halls and churches but cannot support such a massive masonry dome. Option D, corbelled squinches, refers to another method of transitioning from a square to a dome, but Hagia Sophia is specifically noted for its use of pendentives rather than squinch based corbelling.

Common Pitfalls:
Students sometimes confuse pendentives with squinches or assume that any historic church with a large roof must have flying buttresses. Another pitfall is to treat all dome supports as the same. For exam preparation, it is helpful to link each famous example with its key structural innovation, such as pendentives in Hagia Sophia, flying buttresses in Gothic cathedrals, and concrete domes in Roman buildings like the Pantheon.

Final Answer:
The dome of Hagia Sophia is mainly supported by four pendentives resting on massive piers.