The Mutual Ancestry Of Emperor Trajan & Pliny The Younger
The work of Sir Ronald Syme; particularly, his paper titled 'Domitius Corbulo' (JRS, 1970-71), helped in discovering this information.
Pliny The Younger and Emperor Trajan were related to each other through a lady called Vistilia (Sr.) who was born circa 32 BCE. She had 6 different husbands and many children by those husbands. Her first husband was Glitius (Sr.), and they had a child called had Glitius (Jr.). Her second husband was Pomponius Secundus, and they had two children called Q. Pomponius Secundus, and P. Pomponius Secundus (the consul suffect of 44 CE), and he was the grandfather of Pliny The Younger (his mother's father, and father of her brother, Pliny The Elder).
The third marriage of Vistilia Sr. was to Orfitus (Sr.), and they had a child called Orfitus (Jr.). Her fourth husband was (Suillius) Rufus, who was the father of P. Suillius Rufus. After that, she married her fifth husband Domitius Corbulo (Sr.), who was the father of Cn. Domitius Corbulo (consul). Cn. Domitius Corbulo was the grandfather of Emperor Trajan (note that Cn. Domitius Corbulo was married to Cassia Longina, who was a daughter of Emperor Caligula's sister). And her last husband (her sixth) was Octavius (Emperor Augustus Caesar), by whom, she had Milonia Caesonia (who married the emperor Caligula in 40 CE). So in reality, Vistilia (Sextilia) was the common (or mutual) ancestor of many illustrious Roman families.
Pliny The Younger achieved a high position under Trajan, as governor of Bithynia and Pontus. It is highly unlikely the two of them were unaware they were cousins. But that fact appears to have been hidden from the public, just like, it seems, the pretense regarding the persecution of Christians in Pliny's Letters (Epistles).
These two individuals were pretending not to know each other, and so were others within their family.
Pliny may be the individual recorded as C. Salonius Matidius Patrunius, who was married to emperor Trajan's sister, Ulpia Marciana Polla. [Ref. 'Marcus Aurelius: A Biography', by Anthony R. Birley, Published by Yale] Emperor Domitian took Trajan's mother from his father. Trajan then lived within the royal palace with Domitian and his mother, so, Trajan was Domitian's step-son. The Piso family was banished from Rome by Domitian, but Pliny The Younger was not. Pliny's step-father was Lucius Piso when he married Arria The Younger, (Arrius Piso's/Flavius Josephus' mother) when Gaius Piso was forced to commit suicide by Nero. Pliny The Younger would visit Domitian's household, which gave him opportunities to speak with Domitian's wife (Domitia Longina, who was a relative of Pliny's) and Trajan. Pliny hints acting as 'Pope" for a time in Book II, pg. 33, of his Epistles (Loeb Classical Library Edition, Book II of II). He says, "so I feel that I am performing a pious duty." In his works, he stated that for a time, he was the official Roman overseer of religion under Trajan. But realizing that Christianity was created by the Roman and Jewish aristocracy, would make Pliny The Younger Pope for a time.
Emperor Trajan's wife (Arrius Piso's daughter) Claudia Phoebe appears in the New Testament as "our sister Phoebe" in Romans16.1 - as Claudia in II Timothy 4.21 - and as Claudius Ephebus in I Clement LXV.1. Trajan appears as Pudens in II Tim. 4.21 (the same verse as his wife) - and as Fronto in 'Ignatius’' Epistle to the Ephesians II. 1. Their marriage, Claudia Phoebe as Claudia Rufina and Trajan as Pudens, is praised by Valerius Martial (IV. 13). Emperor Trajan's public name was Marcus Ulpius Nerva Trajan (Dio Cassius LXVIII.3(4). Rearranging the letters of Ulpius produces one of his fictional names, Lupus.