The early Church held closed communion and the Romans spied on them and spread rumors

But why need I disparagingly refer to strange spies and informers, when you allege against us such charges as we certainly do not ourselves divulge with very much noise—either as soon as you hear of them, if we previously show them to you, or after you have yourselves discovered them, if they are for the time concealed from you? For no doubt, when any desire initiation in the mysteries, their custom is first to go to the master or father of the sacred rites.  Then he will say (to the applicant), You must bring an infant, as a guarantee for our rites, to be sacrificed, as well as some bread to be broken and dipped in his blood; you also want candles, and dogs tied together to upset them, and bits of meat to rouse the dogs.  Moreover, a mother too, or a sister, is necessary for you. What, however, is to be said if you have neither? I suppose in that case you could not be a genuine Christian. Now, do let me ask you, Will such things, when reported by strangers, bear to be spread about (as charges against us)? It is impossible for such persons to understand proceedings in which they take no part. The first step of the process is perpetrated with artifice; our feasts and our marriages are invented and detailed by ignorant persons, who had never before heard about Christian mysteries. And though they afterwards cannot help acquiring some knowledge of them, it is even then as having to be administered by others whom they bring on the scene. Besides, how absurd is it that the profane know mysteries which the priest knows not!  They keep them all to themselves, then, and take them for granted; and so these tragedies, (worse than those) of Thyestes or Œdipus, do not at all come forth to light, nor find their way to the public. Even more voracious bites take nothing away from the credit of such as are initiated, whether servants or masters. If, however, none of these allegations can be proved to be true, how incalculable must be esteemed the grandeur (of that religion) which is manifestly not overbalanced even by the burden of these vast atrocities! O ye heathen; who have and deserve our pity, behold, we set before you the promise which our sacred system offers. It guarantees eternal life to such as follow and observe it; on the other hand, it threatens with the eternal punishment of an unending fire those who are profane and hostile; while to both classes alike is preached a resurrection from the dead.

Tertullian
Ad Nationes, Book I
Chapter VII

The Real Presence was prefigured in the Old Covenant

When He so earnestly expressed His desire to eat the passover, He considered it His own feast; for it would have been unworthy of God to desire to partake of what was not His own. Then, having taken the bread and given it to His disciples, He made it His own body, by saying, “This is my body,” that is, the figure of my body. A figure, however, there could not have been, unless there were first a veritable body. An empty thing, or phantom, is incapable of a figure. If, however, (as Marcion might say,) He pretended the bread was His body, because He lacked the truth of bodily substance, it follows that He must have given bread for us. It would contribute very well to the support of Marcion’s theory of a phantom body, that bread should have been crucified!  But why call His body bread, and not rather (some other edible thing, say) a melon, which Marcion must have had in lieu of a heart!  He did not understand how ancient was this figure of the body of Christ, who said Himself by Jeremiah: “I was like a lamb or an ox that is brought to the slaughter, and I knew not that they devised a device against me, saying, Let us cast the tree upon His bread,” which means, of course, the cross upon His body. And thus, casting light, as He always did, upon the ancient prophecies, He declared plainly enough what He meant by the bread, when He called the bread His own body. He likewise, when mentioning the cup and making the new testament to be sealed “in His blood,” affirms the reality of His body. For no blood can belong to a body which is not a body of flesh.

…Much more clearly still does the book of Genesis foretell this, when (in the blessing of Judah, out of whose tribe Christ was to come according to the flesh) it even then delineated Christ in the person of that patriarch, saying, “He washed His garments in wine, and His clothes in the blood of grapes”—in His garments and clothes the prophecy pointed out his flesh, and His blood in the wine. Thus did He now consecrate His blood in wine, who then (by the patriarch) used the figure of wine to describe His blood.

Tertullian
The Five Books Against Marcion, Book IV
Chapter XL

God called his body bread

For so did God in your own gospel even reveal the sense, when He called His body bread; so that, for the time to come, you may understand that He has given to His body the figure of bread, whose body the prophet (Jeremiah) of old figuratively turned into bread, the Lord Himself designing to give by and by an interpretation of the mystery.

Tertullian
The Five Books Against Marcion, Book III
Chapter XIX

The sacraments show God’s purpose for the physical world

Indeed, up to the present time, he has not disdained the water which the Creator made wherewith he washes his people; nor the oil with which he anoints them; nor that union of honey and milk wherewithal he gives them the nourishment of children; nor the bread by which he represents his own proper body, thus requiring in his very sacraments the “beggarly elements” of the Creator.

Tertullian
The Five Books Against Marcion, Book I
Chapter XIV

If the heretic’s faith is true, let him prove it by a record of Apostolic succession and full-communion status

But if there be any (heresies) which are bold enough to plant themselves in the midst of the apostolic age, that they may thereby seem to have been handed down by the apostles, because they existed in the time of the apostles, we can say: Let them produce the original records of their churches; let them unfold the roll of their bishops, running down in due succession from the beginning in such a manner that [that first bishop of theirs] bishop shall be able to show for his ordainer and predecessor some one of the apostles or of apostolic men,—a man, moreover, who continued stedfast with the apostles. For this is the manner in which the apostolic churches transmit their registers: as the church of Smyrna, which records that Polycarp was placed therein by John; as also the church of Rome, which makes Clement to have been ordained in like manner by Peter. In exactly the same way the other churches likewise exhibit (their several worthies), whom, as having been appointed to their episcopal places by apostles, they regard as transmitters of the apostolic seed. Let the heretics contrive something of the same kind.

….To this test, therefore will they be submitted for proof by those churches, who, although they derive not their founder from apostles or apostolic men (as being of much later date, for they are in fact being founded daily), yet, since they agree in the same faith, they are accounted as not less apostolic because they are akin in doctrine. Then let all the heresies, when challenged to these two tests by our apostolic church, offer their proof of how they deem themselves to be apostolic. But in truth they neither are so, nor are they able to prove themselves to be what they are not. Nor are they admitted to peaceful relations and communion by such churches as are in any way connected with apostles, inasmuch as they are in no sense themselves apostolic because of their diversity as to the mysteries of the faith.

Tertullian
Against Marcion
The Prescription Against Heretics
Chapter XXXII

Early Christians took Eucharist privately, dismissing anyone else

Since, therefore, the Christians are not their own betrayers, it follows that it must be strangers. Now I ask, how could strangers obtain knowledge of us, when even true and lawful mysteries exclude every stranger from witnessing them, unless illicit ones are less exclusive? Well, then, it is more in keeping with the character of strangers both to be ignorant (of the true state of a case), and to invent (a false account). Our domestic servants (perhaps) listened, and peeped through crevices and holes, and stealthily got information of our ways.

…For no doubt, when any desire initiation in the mysteries, their custom is first to go to the master or father of the sacred rites.

Tertullian
Ad Nationes, Book I
Chapter III

We are taken up from baptism as new-born children

I shall begin with baptism. When we are going to enter the water, but a little before, in the presence of the congregation and under the hand of the president, we solemnly profess that we disown the devil, and his pomp, and his angels. Hereupon we are thrice immersed, making a somewhat ampler pledge than the Lord has appointed in the Gospel. Then when we are taken up (as new-born children), we taste first of all a mixture of milk and honey, and from that day we refrain from the daily bath for a whole week. We take also, in congregations before daybreak, and from the hand of none but the presidents, the sacrament of the Eucharist, which the Lord both commanded to be eaten at meal-times, and enjoined to be taken by all alike.

Tertullian
The Chaplet
Chapter III

Tertullian describes the Agape feast

Yet about the modest supper-room of the Christians alone a great ado is made.  Our feast explains itself by its name.  The Greeks call it agapè, i.e., affection. Whatever it costs, our outlay in the name of piety is gain, since with the good things of the feast we benefit the needy; not as it is with you, do parasites aspire to the glory of satisfying their licentious propensities, selling themselves for a belly-feast to all disgraceful treatment,—but as it is with God himself, a peculiar respect is shown to the lowly. If the object of our feast be good, in the light of that consider its further regulations. As it is an act of religious service, it permits no vileness or immodesty. The participants, before reclining, taste first of prayer to God. As much is eaten as satisfies the cravings of hunger; as much is drunk as befits the chaste.  They say it is enough, as those who remember that even during the night they have to worship God; they talk as those who know that the Lord is one of their auditors. After manual ablution, and the bringing in of lights, each is asked to stand forth and sing, as he can, a hymn to God, either one from the holy Scriptures or one of his own composing,—a proof of the measure of our drinking. As the feast commenced with prayer, so with prayer it is closed. We go from it, not like troops of mischief-doers, nor bands of vagabonds, nor to break out into licentious acts, but to have as much care of our modesty and chastity as if we had been at a school of virtue rather than a banquet.

Tertullian
Apology
Chapter XXXIX

Jesus is both flesh and bread to be eaten

For He was wholly devoted and consecrated to the Lord; so well grown, and to such excessive size, as to reach and extend over all, and to fill those who eat Him and feed upon Him. For He is both flesh and bread, and has given Himself as both to us to be eaten.

Clement of Alexandria
The Stromata, Book VIII
Chapter XI – Fragments from the last work on the Passover