The Trustees and Master Masons

The Town Council and Established Church ministers were named as Trustees. The overseer and supervisor was Heriot's friend, Dr. Walter Balcanquall D.D. Master of the Savoy, Dean of Rochester and later of Durham. Balcanquall was one of the courtier chaplains to both James and Charles I. He was a man of considerable culture, vision and energy, and is believed to have had great influence in the early development of the Hospital. He was instrumental in selecting a field of Slezer Print eight and a half acres – part of the 'Hie Riggs' – to the south of the Castle and Grassmarket, for the site of the building, and he is thought to have advised the master masons on the original design. He was also responsible for the drawing up of the original Statutes, whose influence remains evident in the constitution of George Heriot's Trust and School to this day.

According to Sir John Summerson, in giving "the paterne" to the Hospital, Balcanquall probably indicated the Palace described by Sebastiano Serlio in his "Seventh Book of Architecture" of about 1550. The records make it clear, however, that the architect of Heriot's Hospital was the royal master mason, William Wallace, after whose death in October 1631 the work was carried on by his assistant and successor William Aytoun. Both were experienced Scottish masons who had been involved in working on and studying the construction of other notable buildings in Scotland. It is clear that the main features of the design were laid down at the outset in the ground plan and were adhered to, more or less closely, throughout the undertaking. The result - according to W. Douglas Simpson "as thoroughly a Scottish Building as anything could be" - not only satisfied the practical requirements of a hospital school of its time but has remained as attractive as it is functional to this day.
Aytoun

The Foundation Stone on the north-west tower is inscribed 1 July 1628 and the date is confirmed by contemporary record.

At first, the work of construction progressed rapidly. Stone came from the freestone quarries at Ravelston; lime from Kirkliston and Westhouses; and timber mainly from Dalkeith. Large joists and other commodious timber were imported from Norway, as was not unusual in Scottish building work of this period.

The promising pace of early development was not able to be continued, however. George Heriot's estate had included large sums of money owed to him by the Crown and others, and much delay was encountered in collecting these debts. Further difficulties were caused by the outbreak of the Civil War. By 1650 the building was habitable at last but in that same year it was commandeered by Cromwell's military government in Scotland and converted into an army hospital.