Exhibit 5.1

                                McGuireWoods LLP
                                One James center
                              901 East Cary Street
                               Richmond, VA 23219




                                            April 12, 2002

Markel Corporation
4521 Highwoods Parkway
Glen Allen, Virginia 23060-6148


                               Markel Corporation
                       Registration Statement on Form S-4
                       ----------------------------------

Ladies and Gentlemen:

     Markel Corporation (the "Company"), has requested our opinion in connection
with various legal matters relating to the filing of a Registration Statement on
Form S-4 (the "Registration Statement") under the Securities Act of 1933, as
amended (the "1933 Act"), covering the offer to exchange:

          .    $1,000 principal amount of Markel's Notes due August 15, 2007
               (the "Markel 7.2% Notes") in exchange for each $1,000 principal
               amount of outstanding 7.2% Notes due August 15, 2007 of Terra
               Nova (the "Terra Nova" 7.2% Notes") properly tendered and
               accepted;

          .    $1,000 principal amount of Markel's 7.0% Notes due May 15, 2008
               (the "Markel 7.0% Notes") in exchange for each $1,000 principal
               amount of outstanding 7.0% Notes due May 15, 2008 of Terra Nova
               (the "Terra Nova" 7.0% Notes") properly tendered and accepted.

     The Terra Nova 7.2% Notes and 7.0% Notes are collectively referred to as
the "Terra Nova Notes." The Markel 7.2% Notes, and the Markel 7.0% Notes are
collectively referred to as the "Markel Notes." The exchange will be made
pursuant to the exchange offers (the "Exchange Offers") contemplated by the
Registration Statement.

     We have examined copies of such records of the Company and such other
certificates and documents as we have deemed relevant and necessary for the
opinions hereinafter set forth. In such examination, we have assumed the
genuineness of all signatures, the authenticity of all documents submitted to us
as originals and the conformity to authentic originals of all documents
submitted to us as certified or reproduced copies. We have also assumed the
legal capacity of all persons executing such documents and the truth and
correctness of any representations or warranties therein contained. As to
various questions of fact material to such opinions, we have relied upon
certificates of officers of the Company and of public officials.



Markel Corporation
April 12, 2002
Page 2

     Based upon the foregoing, we are of the opinion that:

          1.   The Company is duly formed and validly existing under the laws of
the Commonwealth of Virginia.

          2.   The Markel Notes will, upon approval by an authorized officer of
Markel and the due issuance and authentication of the Markel Notes and exchange
thereof for the Terra Nova Notes in the manner referred to in the Registration
Statement, constitute valid and binding obligations of the Company, enforceable
against the Company in accordance with their terms, except as enforcement
thereof may be limited by bankruptcy, insolvency, reorganization, fraudulent
conveyance and other similar laws affecting the enforcement of creditors' rights
generally and except as enforcement thereof is subject to general principles of
equity (regardless of whether enforcement is considered in a proceeding in
equity or at law).

     This opinion is limited to the laws of the Commonwealth of Virginia, the
State of New York and the federal laws of the United States of the type
typically applicable to transactions contemplated by the Exchange Offers, and we
do not express any opinion with respect to the laws of any other jurisdiction.

     This letter speaks only as of the date hereof and is limited to present
statutes, regulations and administrative and judicial interpretations. We
undertake no responsibility to update or supplement this letter after the date
hereof.

     We consent to being named in the Registration Statement and related
Prospectus as counsel who are passing upon the legality of the Markel Notes for
the Company and to the reference to our name under the caption "Validity of the
Notes" in such Prospectus. We also consent to your filing copies of this opinion
as an exhibit to the Registration Statement or any amendment thereto. In giving
such consent, we do not admit that we are in the category of persons whose
consent is required under Section 7 of the 1933 Act.

                                                     Very truly yours,


                                                     /s/ McGuireWoods LLP