We start in the Middle Ages, when the falsification of donations was used by religious institutions to retain or acquire new possessions. In this document held at the Archivo Histórico Nacional, and supposedly from the year 570 aD, Alaric donates to Ariol, the abbot of San Julián de Navasal, the towns of Nové and Ardanés with all their possessions, boundaries, and rights, the dwelling of Araniella, and one shift of a day and its night per week in a salt mine located in the town of Salinas.
Very generous; however, different authors consider this document to be one of the crudest forgeries known: the mention of an unknown King Alaric in the second half of the 6th century, making him contemporary with Count Galindo, who held Atarés; or the allusion to Muslims who ruled in Tudela and Huesca, almost 150 years before they set foot on the Peninsula!
Archivo Histórico Nacional, Donation of Alaric to Ariol, the abbot of San Julián de Navasal, 570, available here
Almost four centuries later, here is what was believed to be the oldest document held in the Archivo Histórico de la Nobleza (Historical Archive of the Nobility), dated 26th December 943. The deed states that Count Assur Fernández and his wife, Countess Gontroda, made a donation pro anima to the monastery of San Pedro de Cardeña (Burgos) and its abbot, Cipriano, leaving him the territory of Fuente Adrada, in the jurisdiction of Sacramenia, north of Segovia. If it were indeed the original donation deed, it would have been a noteworthy discovery because it was copied in the Gothic Cartulary of Cardeña, and all the original documents copied in this cartulary, dated around the year 1086, are considered lost. However, a study by the Spanish National Research Council and University of Burgos has demonstrates that the document is actually a forgery from the 12th century. You can find more information and the full transcription of the document at this link.
Archivo Histórico de la Nobleza, Donation of Count Assur Fernández and his wife Countess Gontroda to the monastery of San Pedro de Cardeña (Burgos), 953, avalaible here.
In parallel with the forgeries, counter-fogeries departments developed in the administrations. Remaining with the Spanish case, this 1340 document from the Archivo de la Corona de Aragón is a statement given by Pedro el Ceremonioso to Blas Jiménez de Ayerbe, notary from Huesca, that reassures him of the authenticity about certain documents.
Archivo de la Corona de Aragón, Statement given by Pedro el Ceremonioso to Blas Jiménez de Ayerbe that reassures him of the authenticity about certain documents, available here
Always in Spain, the Royal Chancellery of the Kings of Castile had a dedicated office for forgery investigation: this is a petition dated 1491, by Íñigo de Avío, to the magistrate of Vizcaya, who shall provide oversight regarding certain forgeries committed by certain notaries of Durango, for which the man had suffered severe damages.
Archivo General de Simancas, Forgeries committed by certain notaries of Durango, 1491, available here
In the realm of historical fakes, the one involving relics is a universe unto itself - relics are typically pieces of the bodies of saints, fragments of their clothing, or objects associated with them. They were - and are to these days - considered sacred, and are venerated by believers for their connection to the saint's life or miraculous events. Relics are believed to possess healing powers, or the ability to grant divine favour. Pilgrims travelled (and travel) great distances to visit and venerate them. Naturally, relics also became the object of an entire market of fake objects, sold around or passed off as real in order to improve the power and visibility of a religious congregation; as poet François Mauriac used to say, “with all the original fragments of the cross of Christ that are currently in churches, one could build a ship.” This wood reliquary from the Monastery of La Magdalena, possibly from the 16th-17th century, containing the relics of several saints. In the center, there is a photocopy of a simulated autograph of Saint Teresa of Jesus, dated 1515. Due to the sanctity of Teresa of Jesus, it was a matter of pride for convents and monasteries to possess relics associated with her. In this instance, a counterfeit document was created, mimicking her handwriting.
And again about curious relics and whether they are "real" or not: this is a letter from 1587, describing a series of actions for concessions of Isabel de Hiusen and Catalina de Lizenberg, mothers of the Order of San Francisco, to Manuel Vega Cabeza de Vaca, captain of the Spanish infantry, governor, and envoy of the king of Spain in Germany. The message thanks the governor for his generosity towards their Order, which is compensated with a 30-day period of prayer, fasting, and other spiritual exercises.
Furthermore, the governor was given "a small case in which is fixed a figure of the cross on which our Lord Jesus Christ, health of the world, was hung, from the same place where he was arrested and buried, where he wept for the innocent, not for Mary Magdalene, and then over Jerusalem and Mount Zion with a solicitous soul and great reverence. A treasure that we brought embracing anguish and danger." The case was supposed to preserve the relic of an innocent child slaughtered by Herod.
Archivo Histórico de la Nobleza, Concessions of Isabel de Hiusen and Catalina de Lizenberg, mothers of
the Order of San Francisco, to Manuel Vega Cabeza de Vaca, captain of
the Spanish infantry, governor, and envoy of the king of Spain in
Germany, avalaible
here
These are four certificates of authenticity from Rome, for various relics (pieces of wood from the cross of Christ), between 1560 and 1790.
Despite the drastic law in the medieval Romanian Countries, where the forgery of documents was punished even by death penalty, the desire for wealth led to this kind of practice, regardless of the consequences. One example comes from the National Archives of Romania, which became famous on the national level due to the reputation of the well-known issuer, Mihai Viteazul, the first Romanian ruler able to unite all the three larger Romanian regions, in 1600, for a short period of time.
National Archives of Romania ref. BU-F-01472-438
By this document dated September 27, 1597, Mihai Viteazul gives his mother Tudora (named Teodora after she became a nun) few villages in Oltenia (a historical region in South West Romania), to benefit from them as long as she lives and, after her death, the villages shall pass to his illegitimate daughter – Marula. After Mihai Viteazul’s mother’s death, Marula took the legitime daughter – Florica, who inherited the proprieties of her grandmother according the law – to trial before ruler Alexandru Ilaș, in 1616, bringing this specific document as a proof of her rights. After the investigation was done (even Marula’s mother, the potential former wife of the ruler Mihai Viteazul was interrogated), the ruler decided that „Marula was trying to deceive with this false document”.