The deceased is represented as a warrior: we’re probably to imagine that he was killed in battle. He is shown as a hoplite with equipment typical for this period: wearing a simple tunic, equipped with an Argive shield and a simple conical helmet of pilos type. The latter was in use from about ca. 450 BC and was probably modelled after conical headgear made from felt or some other perishable material. Helmets like this would have been made of bronze.
This hoplite is quite different from what they looked like a few centuries earlier. In the seventh and sixth centuries BC, hoplites typically wore lots of armour: bronze greaves, bronze breastplates or linen corslets, helmets that enclosed the entire head (the Corinthian helmet being the best known example), and so on. A lot of this armour was shed over the course of time. Bronze breastplates were already being replaced by lighter linen corslets towards the end of the sixth century BC. Corinthian helmets went largely into disuse by 450 BC, even though they persisted in art much longer as symbols of a glorious past.
By the time of the Peloponnesian War (431-404 BC), the typical hoplite of the age looked more or less like our man does in this relief. Gone were the many pounds of armour, replaced instead by simpler, lighter, and more affordable equipment. There are many reasons for this, each of which deserves fuller treatment than what I can offer here at present (but our podcast episode on the Greek hoplite is a good starting point, as is my book on Greek warfare).
A very brief explanation for this change is connected to processes of state formation and cities becoming more inclusive. As populations and armies grew, aristocratic warbands of the Archaic period made way for the more centrally-organized and larger armies of the Classical age. With more people being required to fight, the equipment, which the warriors needed to acquire themselves, needed to be cheaper and simpler. This is not to say that hoplites were “poor” or “middling”: these were still relatively well-to-do members of society.
At the same time, during the Classical period, wealthier members of society, men like the Athenian writer Xenophon (ca. 430-354 BC), fought not as hoplites, but as cavalrymen, where there were more possibilities for ostentatious display of wealth, including wearing more bronze armour, such as breastplates, greaves, more elaborate helmets, and various forms of protection for the arms.
Again, this is a greatly simplified summary of a highly complex issue. It’s often easy to look back at the past and think that much of it was unchanging or static. But the reality is that the world is continually changing, and the past was just as dynamic as the present. Greek warfare is just one aspect in which change is noticeable across the centuries.