Thomar has already been seen in the twelfth century when Dom Gualdim Paes built the sixteen-sided church and the castle, and when he and his Templars withstood the Moorish invaders with such success.
As time went on the Templars in other lands became rich and powerful, and in the fourteenth century Philippe le Bel of France determined to put an end to them as an order and to confiscate their goods. So in 1307 the grand master was imprisoned, and five years later the Council of Vienne, presided over by Clement v.—a Frenchman, Bertrand de Goth—suppressed the order. Philippe seized their property, and in 1314 the grand master was burned.
In Portugal their services against the Moors were still remembered, and although by this time no part of Portugal was under Mohammedan rule, Granada was not far off, and Morocco was still to some extent a danger.
Dom Diniz therefore determined not to exterminate the Templars, but to change them into a new military order, so in 1319 he obtained a bull from John xxii. from Avignon constituting the Order of Christ. At first their headquarters were at Castro-Marim at the mouth of the Guadiana, but soon they returned to their old Templar stronghold at Thomar and were re-granted most of their old possessions.
The Order of Christ soon increased in power, and under the administration of Prince Henry, 1417 to 1460, took a great part in the discoveries and explorations which were to bring such wealth and glory to their country. In 1442, Eugenius iv. confirmed the spiritual jurisdiction of the order over all conquests in Africa, and Nicholas v. and Calixtus iii. soon extended this to all other conquests made, or to be made anywhere, so that the knights had spiritual authority over them 'as if they were in Thomar itself.' This boon was obtained by Dom Affonso v. at his uncle Prince Henry's wish.
When Prince Henry died he was succeeded as duke of Vizeu and as governor of the order by his nephew Fernando, the second son of Dom Duarte. Fernando died ten years later and was succeeded by his elder son Diogo, who was murdered fifteen years later by Dom João ii. in 1485. Then the title passed to his brother Dom Manoel, and with it the administration of the order, a position which he retained when he ascended the throne, and which has since belonged to all his successors.
Prince Henry finding that the old Templar church with its central altar was unsuited to the religious services of the order, built a chapel or small chancel out from one of the eastern sides and dedicated it to St. Thomas of Canterbury. But as the order advanced in wealth and in power this addition was found to be far too small, and in a general chapter held by Dom Manoel in 1492 it was determined to build a new Coro large enough to hold all the knights and leaving the high altar in its old place in the centre of the round church.
In all the Templar churches in England, when more room was wanted, a chancel was built on to the east, so that the round part, instead of containing the altar, has now become merely a nave or a vestibule. At Thomar, however, probably because it was already common to put the stalls in a gallery over the west door, it was determined to build the new Coro to the west, and this was done by breaking through the two westernmost sides of the sixteen-sided building and inserting a large pointed arch.
Although it was decided to build in 1492, little or nothing can have been done for long, if it is true that João de Castilho who did the work was only born about the year 1490; and that he did it is certain, as he says himself that he 'built the Coro, the chapter-house—under the Coro—the great arch of the church, and the principal door.'
Two stone carvers, Alvaro Rodrigues and Diogo de Arruda, were working there in 1512 and 1513, and the stalls were begun in July 1511, so that some progress must have been made by them. If then João de Castilho did the work he must have been born some time before 1490, as he could hardly have been entrusted with such a work when a boy of scarcely twenty.