| CCL | Middle of the 3rd century |
| CCLI | Middle of the 3rd century |
| MANETHO | Egyptian priest of the 3rd century BC whose Greek Aegyptiaca (History of Egypt) originated the concept of pharaonic dynasties (7) |
| ARCHIMEDEAN | Relating to the Syracuse-born mathematician of the 3rd century BCE |
| CCC | Last year of the 3rd century |
| EUCLID | Geometrician of the 3rd century BC (6) |
| OSSIAN | Legendary Irish hero and bard of the 3rd Century (6) |
| PERPETUA | Christian martyr of the 3rd century; her comartyr Felicity, was her slave (8) |
| PLOTINUS | Egyptian-born Roman philosopher of the 3rd century AD who founded Neoplatonism (8) |
| CCI | Start of the third century |
| RUNES | The characters of an ancient Germanic alphabet, in use, especially in Scandinavia, from the 3rd Century to the Middle Ages (5) |
| PARTHIA | Country in ancient Asia, southeast of the Caspian Sea, destroyed by the Sassanids in the 3rd century |
| GREATWALL | Defensive structure constructed in the 3rd century BC stretching from the Yellow Sea to the central Asian desert (5,4,2,5) |
| OFCHINA | Defensive structure constructed in the 3rd century BC stretching from the Yellow Sea to the central Asian desert (5,4,2,5) |
| NICE | City on the French Riviera founded by Phocaeans from Marseille in about the 3rd century BC (4) |
| HOURGLASSES | Time-keeping devices thought to have been invented in Alexandria in the 3rd century |
| ORVIETO | City in modern-day Umbria, annexed by Rome in the 3rd Century BCE (7) |
| CRISPIN | Patron saint of shoemakers, martyred in the third century (7) |
| NEOPLATONISM | Originating in the third century. what is the philosophical system generated by Plotinus and his successors? (12) |
| ANTIPOPE | Hippolytus, say, who headed a group opposed to the third-century pontificate of Callixtus I (8) |
