The semis was small Roman bronze

Bronze

Bronze is a metal alloy consisting primarily of copper, usually with tin as the main additive. It is hard and brittle, and it was particularly significant in antiquity, so much so that the Bronze Age was named after the metal...

 coin

Coin

A coin is a piece of hard material that is standardized in weight, is produced in large quantities in order to facilitate trade, and primarily can be used as a legal tender token for commerce in the designated country, region, or territory....

 that was valued at half an as

As (coin)

The , also assarius was a bronze, and later copper, coin used during the Roman Republic and Roman Empire.- Republican era coinage :...

. During the Roman Republic

Roman Republic

The Roman Republic was the period of the ancient Roman civilization where the government operated as a republic. It began with the overthrow of the Roman monarchy, traditionally dated around 508 BC, and its replacement by a government headed by two consuls, elected annually by the citizens and...

, the semis was distinguished by an 'S' (indicating semis) or 6 dots (indicating a theoretical weight of 6 uncia

Uncia (coin)

The uncia was a Roman unit of length and of weight .-Republican coin:...

e). Some of the coins featured a bust of Saturn

Saturn (mythology)

In ancient Roman religion and myth, Saturn was a major god presiding over agriculture and the harvest time. His reign was depicted as a Golden Age of abundance and peace by many Roman authors. In medieval times he was known as the Roman god of agriculture, justice and strength. He held a sickle in...

 on the obverse, and the prow of a ship on the reverse.

Initially a cast coin, like the rest of Roman Republican bronzes, it began to be struck from shortly before the Second Punic War

Second Punic War

The Second Punic War, also referred to as The Hannibalic War and The War Against Hannibal, lasted from 218 to 201 BC and involved combatants in the western and eastern Mediterranean. This was the second major war between Carthage and the Roman Republic, with the participation of the Berbers on...

 (218-204 BC). The coin was issued infrequently during the Roman Empire

Roman Empire

The Roman Empire was the post-Republican period of the ancient Roman civilization, characterised by an autocratic form of government and large territorial holdings in Europe and around the Mediterranean....

, and ceased to be issued by the time of Hadrian

Hadrian

Hadrian , was Roman Emperor from 117 to 138. He is best known for building Hadrian's Wall, which marked the northern limit of Roman Britain. In Rome, he re-built the Pantheon and constructed the Temple of Venus and Roma. In addition to being emperor, Hadrian was a humanist and was philhellene in...

(117-138 AD).