The ancient Greek civilization and roman civilization is interconnected to each other although the interconnection is complicated. The classical Greek art form was to create a sculpture with an ideal artistic form whereas Roman art form was to produce more realistic sculptures and murals. The pre-historians have considered the classic Roman art to be copied from the Greeks with the reference to the Roman sculpture Apollo Belvedere (Copied from a lost bronze original made between 350-325 BC) and Barberini Faun (inspired from the Greek Satyr). The common factor in the ancient Greek and Roman sculptures is the nudity. We also find many of the ancient statues without hands and heads.
Nudity in Roman sculptures:

The concept of Heroic Nudity or Ideal Nudity is conceived by the classical Greek civilization. This concept depicts the mortal human subject as a hero or a demigod. This concept was also applied to women as the women portrayed themselves as Venus and other goddesses. The Roman Goddess Venus and her Greek counterpart Aphrodite was always depicted as nude as a symbol of beauty, although the tradition was to portray respectable women in full clothes. After the 1st century AD, Roman art started
The ancient Roman sculptures also signify the concepts of Pseudo-athlete. This concept describes a sculpture with a combination of an idealized body with a veristic head. The concept of Verism portrayed the subject without any idealizing features with many physical deformities. The ancient Romans used to make the sculpture with realistic heads with ideal bodies. Two of such example is-
• Pseudo-Athlete of Delos:
The male nude sculpture found in the House of Diadomenos on the Greek island Delos. Though the origin of the statue is Roman and it dates back to 100BCE. The veristic head symbolizes the wisdom and experience of the man whereas the perfect idealized body symbolizes the man as a hero, confirming the concept of Heroic Nudity. The sculpture has a draped cloth (Roman Toga) rested across the shoulder as the businessman were not allowed to appear nude in public. Although art historians say that the idealized body is used as a prop for the head. That means in Pseudo-athlete concept, the nude idealized body depicted as a garment.
• Tivoli General:

Tivoli General
At the sanctuary of Hercules, a Pseudo-athlete sculpture of a General, which dates back to 75-50 BCE, was found. The Cuirass at the side of the statue depicts the high rank of the subject of the sculpture. The perfectly youthful semi-nude body is in contrast with his wrinkled, stern face. Both the concept of Heroic nudity and Pseudo-athlete can be seen here.
In medieval time, during the time of Renaissance, the famous sculptor Donatello again started to make the nude sculptures thousands of years after the classic Roman concept of Heroic nudity died. Donatello made the sculpture of the biblical hero David as nude. Several years after Donatello, the maestro Michelangelo made nude arts, reestablishing the tradition of making the biblical heroes as nude.
Why the sculptures are found armless:

armless statue
Historians assume many reasons for why many of the Roman and Greek statues are found with missing arms and heads. One assumption is that, the statues were widely transported (a lot of ancient Greek statues were transferred to Rome, which was the capital of the Emperor), or got robbed like a hundred times spanning more than three thousand years, so that the weak points of the statue like the hands, head or sometimes the penises of the statue got broken. Maybe the broken parts were lost immediately during transportation or it was later reattached to the body but it broke again due to the course of time.
Another theory states that the statues survived during the middle age, where many battles were fought almost everywhere in Italy. The massive vandalism happened during middle age known as Western Christendom which caused the religion fanatics to destroy the ancient Roman religion (Paganism) to fall down. But most of the statues survived because of the pagan care and Christian ignorance.
When the famous statue Venus de Milo was dug up, it was unaffected. Its hands fell off sometimes after the discovery. The statue is now on display in Louvre museum.
Sometimes the statues were destroyed for political reasons.