Nero, Rome mint imitation, fake Sestertius, 20th century cast, cf. RIC 324.

Nero, Rome mint imitation, (5th emission), 20th century cast, genuine pieces struck ca. 66 AD.,
fake Sestertius (ø 31-32 mm / 24,52 g), brass ("orichalcum"), axes about coin alignment ↑↓ (ca. 200°),
Obv.: IMP NERO CLAVD CAESAR AVG GER P M TR P P P , his laureate head facing left (RIC obverse type 71 G)
Rev.: PACE P R TERRA MARIQ PARTA IANVM CLVSIT / S - C , temple of Janus with doors closed to r., with latticed window to left, and garland hung across closed double doors on the right.
for genuine pieces cf. RIC I², p. 169, no. 324 (scarce) ; - BMC 163 ; - Mac Dowall, Nero (WCN) 165 ; - CBN 418 ; - Coh. 162 .

rough surface, casting bubbles, weak outlines, some tooling below (modern?) patination (below bust truncation, below temple), unusual obverse die (not found online)

In ancient Rome, the main Temple of Janus stood in the Roman Forum near the Argiletum. Numa built the Ianus geminus (also Janus Bifrons, Janus Quirinus or Portae Belli), a passage ritually opened at times of war, and shut again when Roman arms rested. It formed a walled enclosure with gates at each end, situated between the old Roman Forum and that of Julius Caesar, which had been consecrated by Numa Pompilius himself. About the exact location and aspect of the temple there has been much debate among scholars. It had doors on both ends, and inside was a statue of Janus, the two-faced god of boundaries. The Temple doors (the "Gates of Janus") were closed in times of peace and opened in times of war.
According to Livy 1.19 the second king of Rome, Numa Pompilius, decided to distract the early, warlike Romans from their violent ways by instilling in them awe and reverence. His projects included promoting religion, certain priesthoods, and the building of temples as a distraction with the beneficial effect of imbuing spirituality. The Temple of Janus was Numa's most famous temple project.
During Numa's reign, the Gates of the Temple of Janus were closed and Rome remained at peace. The next king, Tullus Hostilius, opened the Gates of Janus when he went to war with Alba Longa. The Gates of Janus remained open for the next 400 years until after the First Punic War when T. Manlius Torquatus closed the Gates of Janus in 235 BC. This closure lasted about eight years. War with the Gauls in Northern Italy forced the Gates of Janus to reopen. They did not close again until 29 BC, following the deaths of Antony and Cleopatra.
The exact date of the third closure remains a scholarly debate. The only ancient author to date the third closure was Orosius, who associates the event with the birth of Christ, ca. 1 BC. However, modern scholars almost universally reject Orosius because Roman armies were campaigning in Germany and/or the Far East elsewhere by 2 BC. Inez Scott Ryberg and Gaius Stern date the third closure to 13 BC based on the joint return of Augustus and Agrippa to Rome after pacifying the provinces. Sir Ronald Syme dated the closure to 7 BC, to coincide with the triumph of Tiberius and his second consulship, the events of which year are lost in a gap in the surviving manuscripts of Cassius Dio. Mario Torelli followed Orosius' date.
Later emperors also closed the Gates of Janus to great fanfare. The most famous closures occurred under Nero and Vespasian. Nero minted a large series of coins with the Ara Pacis (and the Temple itself with closed gates) on the reverse to commemorate this event. Other emperors certainly closed and reopened the Gates of Janus, but references in later and less thorough historians are fairly rare.

more on https://en.wikipedia.org/wiki/Temple_of_Janus_(Roman_Forum) , https://en.wikipedia.org/wiki/Janus