The "zombies" walking around in Jerusalem after Jesus' death

The tombs also were opened. And many bodies of the saints who had fallen asleep were raised, and coming out of the tombs after his resurrection they went into the holy city and appeared to many. Matthew 27:52-53

Critics will say this means "zombies" roamed the earth at this time.

However, interpreting this as resurrected people walking around in Jerusalem after Jesus' death makes the most sense when

1) the Jewish historical/cultural milieu,

2) the messianic mission of Jesus,

3) the OT prophetic writings about the Messiah and Matthew' Jewish-oriented literary mission are taken into consideration.

First, in a major section of Jewish thought of the day, the bodily resurrection of OT Jewish saints would occur when the messiah came. They literally expected a bodily resurrection (like that in the passage under discussion) to occur at the revealing of the messiah... Indeed, one rabbi was recorded as saying this:

"R. Jeremiah commanded, 'When you bury me, put shoes on my feet, and give me a staff in my hand, and lay me on one side; that when Messias comes I may be ready."(Lightfoot, _Commentary of the New Testament from the Talmud and Hebraica)

Much of such rabbinical lore had an element of truth in it; and this was no exception...the Messiah did produce some resurrections of some of the saints--but only as a first-fruits of His work... So, in keeping with Matthew's Jewish-focused message, it makes sense for him to record this action of the Messiah. This event actually does mesh with the general topics in NT teachings: Jesus teaching about resurrection to Mary in John; the Christ as first fruits in Paul; and Christ leading 'captivity captive' (OT saints in Sheol released at the atonement)...

These types of resurrection people (probably in normal form, like Lazarus was raised) form the basis for one argument of the first apologists of the faith, Quadratus. He was a very early 2nd century apologist (writing sometime during the reign of Hadrian), and we have only one fragment of his: "But our Savior's works were permanent, for they were real. Those who had been cured or rose from the dead not only appeared to be cured or raised but were permanent, not only during our Savior's stay on earth, but also after his departure. They remained for a considerable period, so that some of them even reached our times." (Greek Apologists of the Second Century, Robert M. Grant, Westminster: 1988)

Now it would be highly unusual for someone raised in 33 ad to live naturally another 90-100 years (to the times of Quadratus' writings) but this is not necessarily the scope of his reference to 'our times'...this latter phrase could often mean plus-or-minus 50-75 years, allowing these saints to die naturally again (as would have the resurrected Lazarus, the widow's son, etc.) after a few decades. The point is that resurrections are not isolated phenomena--they were a bit more widespread than the few individual cases mentioned in the gospels would lead us to believe...Eutychus by Paul, the group at the Crucifixion--indeed, even Ireneaus--a half century later--could write of resurrections in Christian Churches (Against Heresies 2.32.4)...

Indeed, stories of these risen saints circulated over time. They show up in several of the NT apocryphal works (e.g. The Greek Apocalypse of Ezra 7.1-2, Gospel of Nicodemus 17ff). For example, in this later work (Gospel of Nicodemus/Acts of Pilate), there is the story of Simeon and his sons (living in Arimathea), who were raised at that time, whose tombs were still open (for inspection?), and who wrote sworn testimony to their resurrection. While many of these stories are no doubt might be embellishments of the passage in Matthew (apocryphal writings generally "filled in the gaps" left by the biblical writers), there may be some historical core behind such related stories as this one about Simeon.

Paul's argument in Col 2.15:" And having disarmed the powers and authorities, he made a public spectacle of them, triumphing over them by the cross." might find a reference to this 'public' display of the resurrection power of Jesus. Its tight coupling in the narrative with the torn veil, suggests that it too is part of the dramatic display of God's 'change of program' for His people...no longer is access to God 'covered with a veil' and no longer are His saints covered with 'the veil of death'... It is this last point that tips us off to what Matthew is likely demonstrating/pointing out in this passage: that the rising/appearing of the saints is intimately connected with both the literary texture of the passage and with the ministry of the Jewish Messiah...

The connection with the preceding image (i.e. the earthquake and rocks) shows up in the Jewish connection between the two in the thought of the day. So Raymond Brown, in The Death of the Messiah, gives us the archeological background:

The connection of the tomb openings with the preceding rending of the rocks is visible in the Dura Europos synagogue wall-paintings that portray the raising of the dead as part of the enlivening of the dry bones in Ezek 37--a 3d-cent. AD tableau that is very helpful in understanding how Matt and/or his readers might imagine the scene he is narrating. There in the splitting of a mountain covered by trees (almost surely the Mount of Olives rent by an earthquake), rocks are rent, thus opening up tombs burrowed into the sides of the mountain and exposing bodies of the dead and their parts. A figure is depicted who may be the Davidic Messiah (see Ezek 37:24-25) bringing about this raising of the dead. Earlier and contemporary with the writing of Matt there is testimony to the importance that Ezek 37 had for the just who died for their convictions about God. At Masada, where Jewish Zealots made their last stand against the Roman armies in AD 73, in the floor of the synagogue were found fragments of a scroll on which was written Ezekiel's account of his vision of the raising of the dead bones. Consequently, even apart from the Dura Europos picturization, Ezek 37:12-13 may be the key passage behind Matt's description both in this line and in what follows, for it offers the only opening of tombs (as distinct from the simple raising of the dead) described in the OT. The people of God are assured that they will come to know the Lord because: "I will open your tombs [mnema], and I will bring you up out of your tombs, and I will lead you into the land of Israel."

Its connection with the messianic ministry of Jesus (of primary concern to Matthew) is also seen:

The coming of the kingdom of God in the ministry of Jesus was understood not as the final manifestation of the kingdom (i.e., the culmination when the Son of Man would gather before him all the nations, assigning those who are to inherit the kingdom prepared for them from the foundation of the world, as in 25:31-34) but as an inbreaking inaugurating and anticipating it. Similarly, this raising of "many bodies" as Jesus dies is not the universal final resurrection but an inbreaking of God's power signifying that the last times have begun and the judgment has been inaugurated. [The Death of the Messiah, Brown]

And finally, its connection with the presentation motif of Matthew (i.e. relating the events surrounding the life and ministry of Jesus to its OT background) is seen through the explicit Ezekiel imagery:

Matt's second motive in adding v. 53 was the fulfillment of Scripture. Above I pointed out how much Ezek 37 with its creative description of the enlivening of the dry bones influenced Jewish imagination in picturing the resurrection of the dead. The first part of Ezek 37:12-13, "I will open your tombs," probably shaped the third line of the quatrain of Matt 27:51b-52b, "And the tombs were opened." But the Ezek passage continues: "And I will bring you up out of your tombs, and I will lead you into the land of Israel. Then you shall know that I am the Lord." Even as elsewhere Matt enhances the scriptural background and flavoring of material taken from Mark, so here scripturally he goes beyond the quatrain by offering in 27:53 the fulfillment of the rest of the Ezek passage: "And having come out from the tombs, . . . they entered into the holy city [of Jerusalem]." Another biblical passage may have shaped Matt's addition, especially the last clause "and they were made visible to many," i.e., Isa 26:19 (LXX): "Those in the tombs shall be raised, and those in the land [or on the earth] shall rejoice." Thus in what he has added to Mark (both the quatrain taken over from popular tradition and his own commentary on it), Matt has developed the theological insight. In apocalyptic language and imagery borrowed from Scripture he teaches that the death of Jesus and his resurrection ("raising") marked the beginning of the last times and of God's judgment...[The Death of the Messiah, Brown]

Thus, the passage finds connection with

1) the Jewish milieu,

2) the messianic mission of Jesus, and

3) the OT prophetic writings about the Messiah.

Far from being simply 'stuck on', it is very much a part of the Jewish context in which Jesus ministered and in which Matthew wrote. Overall, the passage makes the theological connections clear for the reader. Brown summarizes this well, noting that this small passage...

...offered a dramatic way in which ordinary people familiar with OT thought could understand that the death of Jesus on the cross had introduced the day of the Lord with all its aspects, negative (divine wrath, judgment) and positive (conquest of death, resurrection to eternal life).'

Also, it should be quite clear as to why it did not show up in Luke-writing to the Gentiles, and in Mark: It would not have been relevant to their literary purposes.

Thus, this is not some off the wall "zombie" story, as some critics charge; when taking the historical/cultural/theological/literary context of the original author/readers into consideration and not anachronistic interpretations or naturalistic assumptions. The former since this is the standard for all works, and the latter only applies if their ontological view can be proven.