That there was a darkness lasting three hours during the crucifixion is recorded in three of the Gospels. They read as follows:
Matthew 27:45 Now from the sixth hour there was darkness over all the land unto the ninth hour.
Mark 15:33 And when the sixth hour was come, there was darkness over the whole land until the ninth hour.
Luke 23:44-48 And it was about the sixth hour, and there was a darkness over all the earth until the ninth hour.
45 And the sun was darkened, and the veil of the temple was rent in the midst.
46 And when Jesus had cried with a loud voice, he said, Father, into thy hands I commend my spirit: and having said thus, he gave up the ghost.
47 Now when the centurion saw what was done, he glorified God, saying, Certainly this was a righteous man.
48 And all the people that came together to that sight, beholding the things which were done, smote their breasts, and returned.
There are a number of interesting discussions available on the Internet about what would have caused the three hours of darkness. A solar eclipse would not have lasted for three hours. During the last three hours of Jesus’ sacrificial death on the cross, an eerie darkness struck the land. This darkness is documented by the Gospel writers Matthew, Mark, and Luke as indicated above. It is also confirmed by three extra-biblical historians: Thallus, Phlegon, and Africanus.
Thallus wrote a history of the eastern Mediterranean world since the Trojan War. Thallus wrote his regional history in about AD 52. Although his original writings have been lost, he is specifically quoted by Julius Africanus, a renowned third century historian. Africanus states, ‘Thallus, in the third book of his histories, explains away the darkness as an eclipse of the sun—unreasonably as it seems to me.’ Apparently, Thallus attempted to ascribe a naturalistic explanation to the darkness during the crucifixion.
Phlegon was a Greek historian who wrote an extensive chronology around AD 137:
In the fourth year of the 202nd Olympiad (i.e., AD 33) there was ‘the greatest eclipse of the sun’ and that ‘it became night in the sixth hour of the day [i.e., noon] so that stars even appeared in the heavens. There was a great earthquake in Bithynia, and many things were overturned in Nicaea.’
Phlegon provides powerful confirmation of the Gospel accounts. He identifies the year and the exact time of day. In addition, he writes of an earthquake accompanying the darkness, which is specifically recorded in Matthew’s Gospel (Matthew 27:51). However, like Thallus, he fallaciously attempts to interpret the darkness as a direct effect of a solar eclipse.
Africanus composed a five volume History of the World around AD 221. He was also a pagan convert to Christianity. His historical scholarship so impressed Roman Emperor Alexander Severus that Africanus was entrusted with the official responsibility of building the Emperor’s library at the Pantheon in Rome. Africanus writes:
On the whole world there pressed a most fearful darkness; and the rocks were rent by an earthquake, and many places in Judea and other districts were thrown down. This darkness Thallus, in the third book of his History, calls, as appears to me without reason, an eclipse of the sun. For the Hebrews celebrate the passover on the 14th day according to the moon, and the passion of our Saviour falls on the day before the passover; but an eclipse of the sun takes place only when the moon comes under the sun. And it cannot happen at any other time but in the interval between the first day of the new moon and the last of the old, that is, at their junction: how then should an eclipse be supposed to happen when the moon is almost diametrically opposite the sun? Let opinion pass however; let it carry the majority with it; and let this portent of the world be deemed an eclipse of the sun, like others a portent only to the eye. Phlegon records that, in the time of Tiberius Caesar, at full moon, there was a full eclipse of the sun from the sixth hour to the ninth—manifestly that one of which we speak. But what has an eclipse in common with an earthquake, the rending rocks, and the resurrection of the dead, and so great a perturbation throughout the universe? Surely no such event as this is recorded for a long period.
Africanus rightly argues that a solar eclipse could not have occurred during the lunar cycle of the Passover. He also questions the link between an eclipse, an earthquake, and the miraculous events recorded in Matthew’s Gospel. Eclipses do not set off earthquakes and bodily resurrections. We also know that eclipses only last for several minutes, not three hours. For Africanus, naturalistic explanations for the darkness at the crucifixion were grossly insufficient, as he showed by applying real science.
Tertullian, in his Apologeticus, told the story of the crucifixion darkness and suggested that the evidence must still be held in the Roman archives.
I found the following discussion interesting as responded to by Dr. William Craig of Reasonable Faith: http://www.reasonablefaith.org/thallus-on-the-darkness-at-noon
Matt Slick from carm.org also has the following comments: https://carm.org/there-non-biblical-evidence-day-darkness-christs-death
Another little gem I ran into is confirmation of earth quake damage to the Temple:
“The Israel Exploration Journal published by the institute of archeology at the Hebrew University published an article “Earthquakes in Israel and Adjacent Areas: Macrosismic Observations since 100 BCE.” On page 265 they list a slight earthquake in Jerusalem in AD 30 and one in AD 33 which affected Judea, Jerusalem including damage to the temple.”