In classical Greek architecture, particularly in the Doric order, the frieze is a horizontal band part of the entablature, located above the architrave and below the cornice.
The Doric frieze is characterized by an alternating series of two elements:
Triglyphs: Rectangular blocks with three vertical grooves (glyphs). They are thought to be stylized representations of the ends of wooden beams in earlier timber temples. Triglyphs are typically centered over columns and over the space between columns.
Metopes: Square or rectangular panels located between the triglyphs.
Purpose of the Metope:
Decorative Element: The primary purpose of metopes in the Doric frieze was to fill the spaces between triglyphs and to provide surfaces for decoration.
Sculptural Reliefs: Metopes were often decorated with painted scenes or, more famously, with sculptural reliefs depicting mythological subjects (e.g., battles of Lapiths and Centaurs, Labors of Herakles, Trojan War scenes, as seen on the Parthenon). (This relates to option a, but the metope itself is the panel that *receives* the sculpture, serving a decorative role in the sequence).
Structural Origin (Theorized): Some theories suggest that in early timber construction, the spaces between the beam-ends (represented by triglyphs) might have been open or filled with plain panels. Over time, these panels (metopes) became a field for artistic expression.
Let's evaluate the options:
(a) To frame sculptures depicting mythological scenes: While metopes often contained such sculptures, their function within the frieze's rhythm is as a panel between triglyphs. The "framing" is part of this. This is a strong aspect of their use.
(b) To channel rainwater away from the roof: Rainwater management was handled by the cornice, gutters (sima), and spouts (gargoyles), not by metopes in the frieze.
(c) To support the weight of the roof: The primary structural load of the roof is carried by the columns, architrave, and then distributed through the entablature. Metopes are infill panels in the frieze; they are not primary load-bearing structural elements for the roof itself, though the frieze as a whole is part of the entablature that supports the cornice and roof structure.
(d) To serve as a decorative element between triglyphs: This accurately describes the role of metopes. They alternate with triglyphs to form the characteristic pattern of the Doric frieze, and these panels were typically decorated.
Considering the options, (d) provides the most direct and encompassing description of the metope's purpose within the frieze structure. Option (a) describes *what* was often on the metopes, which supports their decorative function. The key is that they are decorative panels situated *between triglyphs*.
\[ \boxed{\text{To serve as a decorative element between triglyphs}} \]