Almost all the men in the movie are shown wearing trousers, which would not come to exist in the Mediterranean for another 600 years, and which the Ancient Greeks never wore, preferring to opt for loose-fitting, draped clothing (it was not until the late Roman Republic, c. 100BC, that trousers came to be commonly worn in the northern Mediterranean).
A main character, the thief, is named Stavros. Although this is one of the most common names in modern Greece, it would have been unknown as a name for a person in pre-Christian times. Stavrós means cross in Greek, referring to the death of Jesus.
When people are being evacuated from Theseus' village, one of the carts used has modern (post-1900) bicycle wheels, complete with metal spokes (painted black) laced in a cross 3 pattern and chrome plated double flanged hubs. These would not be seen until the start of the 20th century.
Most of the armaments used in this film are from a long while later. The apple-core swords used at the end are more Late Roman, not Archaic Greek, and the curved, scimitar-like swords used by the enemy first appeared in Central Asia during the Middle Ages.
The decoration throughout the film was anachronistic. The busts and some of the pots were of a style not seen until the late Hellenistic, about a thousand years after the film is set; the painting on the wall near the end is of a style not seen until about 650BC, and then only on pots, since it was made using thin clay slip which turned black during firing, rather than using paint, which a wall-painting would have used.
The film is supposedly set in the bronze age, but the soldiers use a silvery metal, presumably iron or steel, for their weapons and armor. Iron is also used in braziers. In the bronze age, braziers or portable fires would have been made from ceramic material.
Before the final battle, Theseus vigorously climbs up a rusty metal ladder to a higher part of the defense wall and to give an encouraging speech to his men. The metal ladder is made from welded steel construction pipes (HSS or hollow structural section). Structural steels was first used in the 1700's and the process of welding used was first discovered in 1802 AD.
Helios is seen getting water from what appears to be a cast-iron pipe that looks to serve as the village water supply. Quite apart from cast-iron being unknown in the BRONZE Age, closed metal plumbing such as that depicted did not exist until the 19th Century, some 3,000 years after the era the movie is set in.
On the morning of the battle, when Hyperion walks to the front of his army set to attack, all his soldiers are wielding their weapons in their left hand, shields on their right. When the shot switches to the front, all the soldiers have their weapons in their right hand.
King Hyperions men are incorrectly referred to as "Heraklions". The city of Heraklion was founded in 824AD, 2,000 years after the setting of the movie. Hyperion and his men should instead be called "Minoans", which was the culture of the time for the region Hyperion is suggested to come from (i.e. Crete). Similarly, the "Hellenics" should be referred to as "Helladics", for the same reasons; "Hellenic" refers to a much later period of Greek history (323BC to 146BC).
In one scene, several characters are biting pieces of PC-52 steel reinforcing bars (first used around 1700 AD). However, this is the prison constructed by the Gods to imprison the Titans. As a magical construct, it doesn't necessarily conform to any real world materials or follow real world physics. This may be true, but there was re-bar used throughout the film. Not just in the presence of the Titans.
The goof items below may give away important plot points.
When Theseus is about to kill King Hyperion, both Mickey Rourke's eyes are the same original color. However, Hyperion's character has his left eye mutilated throughout the film and the eye (surrounded by his scar) looks gray/greenish, until the very last scene.
When Theseus takes his mother's body into the temple he cuts his right leg and walks in bare feet, but moments later when he's fighting the beast with the barbed wire helmet he has gladiator-style sandals on. He has no shoes on, on the way in deliberately to leave a trail, although not shown one can infer he had shoes with him as well by the way he followed his foot-trails on the way out as he never ventured into the maze with his mother to honor the gods prior to her death, thus would not have known the way out. Furthermore, this is probably a sly allusion to the method (a ball of string) that Theseus used to escape from the labyrinth according to ancient mythology.
When Theseus gives his "Henry V speech", the soldiers repeatedly bang their shields in agreement. Several of the soldiers are a little too enthusiastic and it can be clearly seen that the silver spray paint covering their shields is tearing off. One soldier (middle-left) has almost completely stripped the top-left section of his plastic "shield."