This is a 'potted' history about the Saints Cosmus(sic) and Damian taken from various sources.
According to Christian traditions, Saints Cosmas and Damian (also written Kosmas and Damianos) (died ca. 287) were twin brothers, physicians, and early Christian martyrs born in Cilicia, part of today's Turkey. They practiced their profession in the seaport of Ayas, Adana, then in the Roman province of Syria. Accepting no payment for their services led to them being named "Unmercenary"; it has been said that, by this, they attracted many to the Christian faith.
According to Christian traditions, during the persecution under Diocletian, Cosmas and Damian were arrested by order of the Prefect of Cilicia, one Lysias who is otherwise unknown, who ordered them under torture to recant. However, according to legend they stayed true to their faith, enduring being hung on a cross, stoned and shot by arrows and finally suffered execution by beheading. Anthimus, Leontius and Euprepius, their younger brothers, who were inseparable from them throughout life, shared in their martyrdom.Their most famous miraculous exploit was the grafting of a leg from a recently deceased Ethiopian to replace a patient's ulcered or cancerous leg, and was the subject of many paintings and illuminations.
According to the source 'New Advent' editor Kevin Knight
Sts Cosmas and Damian were early Christian physicians and martyrs whose feast is celebrated on 27 September. They were twins, born in Arabia, and practised the art of healing in the seaport Ægea, now Ayash (Ajass), on the Gulf of Iskanderun in Cilicia, Asia Minor, and attained a great reputation. They accepted no pay for their services and were, therefore, called anargyroi, "the silverless". In this way they brought many to the Catholic Faith.
When the Diocletian persecution began, the Prefect Lysias had Cosmas and Damian arrested, and ordered them to recant. They remained constant under torture, in a miraculous manner suffered no injury from water, fire, air, nor on the cross, and were finally beheaded with the sword. Their three brothers, Anthimus, Leontius, and Euprepius died as martyrs with them.
The execution took place 27 September, probably in the year 287. At a later date a number of fables grew up about them, connected in part with their relics. The remains of the martyrs were buried in the city of Cyrus in Syria; the Emperor Justinian I (527-565) sumptuously restored the city in their honour. Having been cured of a dangerous illness by the intercession of Cosmas and Damian, Justinian, in gratitude for their aid, rebuilt and adorned their church at Constantinople, and it became a celebrated place of pilgrimage. At Rome Pope Felix IV (526-530) erected a church in their honour, the mosaics of which are still among the most valuable art remains of the city.
The Greek Church celebrates the feast of Saints Cosmas and Damian on 1 July, 17 October, and 1 November, and venerates three pairs of saints of the same name and profession. Cosmas and Damian are regarded as the patrons of physicians and surgeons and are sometimes represented with medical emblems. They are invoked in the Canon of the Mass and in the Litany of the Saints.
There are many depictions of Sts Cosmas and Damian some of which I have included on this page. The spelling Cosmus we use seems to be a corruption of the accepted spelling although the name Cosmo is also used. churches dedicated to these two saints are quite rare, those in the UK are :-
Blean, Kent, church of St Cosmus and St Damian in the Blean;
Keymer, Sussex, St Cosmas and St Damian Church, Keymer;
Sherrington, Wiltshire, church of St Cosmo and St Damian, in the Benefice of the Upper Wylye Valley;
Stretford, near Leominster, Herefordshire, church no longer in use and in the care of the Churches Conservation Trust.
There are also some in France:-
Saint Côme-Saint Damien church, Luzarches, Val d'Oise, France
Saint Côme-Saint Damien church, Paris, France
Saint Côme-Saint Damien church, Chamboulive, France
Saint Côme-Saint Damien church, Serdinya, France
The cult of the two martyrs, SS. Cosmas and Damian, grew rapidly: it began as early as the fourth century when churches were dedicated to them in Jerusalem, in Egypt and in Mesopotamia. Saints' names were adopted from a desire to venerate and emulate their achievements. According to Theoderet, quoted by Delehaye, the trivial remains of St.Cosmas were dispersed and divided in the fourth century. "Both Proclus (A.D.443-447) and Justinian (Emperor,A.D.527-565) erected churches to the saints. Justinian brought the relics to Byzantium. They were next heard of in Rome where in the Via dei Foro Imperiali, St. Felix (Pope A.D. 526-530), utilizing a hall of the Forum of Vespasian and adding an apse, established a church in honour of the two saints: this still contains brilliant sixth-century mosaics in which the saints figure.
The Apse of the Church of Saints Cosmas and Damian, Rome
Mosaic, 7th century
Since 1581 the skulls of the two saints have reposed in the Convent of the St.Claire Nuns of Madrid, where they have been objects of veneration.They had been removed from Rome to Bremen in the tenth century, then to Bamberg, and finally to Madrid by order of the Empress Maria, daughter of the Emperor Charles V. In 1935 scientific examination of the skulls showed that their martyrdom must have taken place late in life,i.e. above the age of fifty, as shown by the state of obliteration of the sutures.
Reliquary located in Saint Michael's Church in Munich, Germany has two doors that open to display the saints' skulls
This, the mother church of England, was begun in 1070 by Lanfranc, the first Norman Archbishop. Reconstruction went on from 1096 to 1107 and it was consecrated in 1130. Amongst the many relics deposited in movable feretra (iron relic chests), listed in the inventory of A.D. 1315, were those of many saints, including bones of SS.Cosmas and Damian. 'Inferetrocum Crucifixio eburneo continentur de ossibus Sanctorum Cosme et Damiani martyrum.' A further mention of relics of these saints reads:'Incistulaeburneaquadratacum serura de Cupro continentur [square ivory box with copper lock] maxille Sanctorum Cosme et Damian icum ixdentibus. Thus it was claimed that not only were there bones of the two saints but also their jawbones and nine teeth.