But the steps which Elizabeth had taken made it necessary to go further. If the Protestants were the less numerous, they were the abler and the more vigorous party, and the break with Rome threw Elizabeth, whether she would or no, on their support. It was a support that could only be bought by theological concessions, and above all by the surrender of the Mass; for to every Protestant the Mass was identified with the fires of Smithfield, while the Prayer-Book which it had displaced was hallowed by the memories of the Martyrs. The pressure of the reforming party indeed would have been fruitless had the Queen still been hampered by danger from France. Fortunately for their cause the treaty of Cateau-Cambrésis at this juncture freed Elizabeth's hands. By this treaty, which was practically concluded in March 1559, Calais was left in French holding on the illusory pledge of its restoration to England eight years later; but peace was secured and the danger of a war of succession, in which Mary Stuart would be backed by the arms of France, for a while averted. Secure from without, Elizabeth could venture to buy the support of the Protestants within her realm by the restoration of the English Prayer-Book. Such a measure was far indeed from being meant as an open break with Catholicism. The use of the vulgar tongue in public worship was still popular with a large part of the Catholic world; and the Queen did her best by the alterations she made in Edward's Prayer-Book to strip it of its more Protestant tone. To the bulk of the people the book must have seemed merely a rendering of the old service in their own tongue. As the English Catholics afterwards represented at Rome when excusing their own use of it, the Prayer-Book "contained neither impiety nor false doctrine; its prayers were those of the Catholic Church, altered only so far as to omit the merits and intercession of the saints." On such a concession as this the Queen felt it safe to venture in spite of the stubborn opposition of the spiritual estate. She ordered a disputation to be held in Westminster Abbey before the Houses on the question, and when the disputation ended in the refusal of the bishops to proceed, an Act of Uniformity, which was passed in spite of their strenuous opposition, restored at the close of April the last Prayer-Book of Edward, and enforced its use on the clergy on pain of deprivation.