Exhibit 24

                                POWER OF ATTORNEY

        Know all by these present, that the undersigned hereby constitutes and
appoints Christopher K. Dalrymple the undersigned's true and lawful
attorney-in-fact to:

        (1)     execute for and on behalf of the undersigned, in the
                undersigned's capacity as a director or officer of Alleghany
                Corporation (the "Corporation"), Forms 3, 4, and 5 in accordance
                with Section 16(a) of the Securities Exchange Act of 1934 and
                the rules thereunder;

        (2)     do and perform any and all acts for and on behalf of the
                undersigned which may be necessary or desirable to complete and
                execute any such Form 3, 4, or 5 and timely file such form with
                the United States Securities and Exchange Commission and any
                stock exchange or similar authority; and

        (3)     take any other action of any type whatsoever in connection with
                the foregoing which, in the opinion of such attorney-in-fact,
                may be of benefit to, in the best interest of, or legally
                required by, the undersigned, it being understood that the
                documents executed by such attorney-in-fact on behalf of the
                undersigned pursuant to this Power of Attorney shall be in such
                form and shall contain such terms and conditions as such
                attorney-in-fact may approve in such attorney-in-fact's
                discretion.

        The undersigned hereby grants to such attorney-in-fact, full power and
authority to do and perform any and every act and thing whatsoever requisite,
necessary, or proper to be done in the exercise of any of the rights and powers
herein granted, as fully to all intents and purposes as the undersigned might or
could do if personally present, with full power of substitution or revocation,
hereby ratifying and confirming all that such attorney-in-fact shall lawfully do
or cause to be done by virtue of this power of attorney and the rights and
powers herein granted. The undersigned acknowledges that the foregoing
attorney-in-fact, in serving in such capacity at the request of the undersigned,
is not assuming, nor is the Corporation assuming, any of the undersigned's
responsibilities to comply with Section 16 of the Securities Exchange Act of
1934.

     This Power of Attorney shall remain in full force and effect until the
     undersigned is no longer required to file Forms 3, 4, and 5 with respect to
     the undersigned's holdings of and transactions in securities issued by the
     Company, unless earlier revoked by the undersigned in a signed writing
     delivered to the foregoing attorney-in-fact.

     IN WITNESS WHEREOF, the undersigned has caused this Power of Attorney
     to be executed as of this 8th day of March, 2012.

                                        Name: /s/ Stephen P. Bradley
                                              ----------------------------
                                              Stephen P. Bradley