Fifth Supplemental Indenture

Exhibit 4.2

MARKEL CORPORATION

Issuer

TO

THE BANK OF NEW YORK MELLON

(as successor to The Chase Manhattan Bank)

Trustee

Fifth Supplemental Indenture

Dated as of September 22, 2009

$350,000,000

7.125% Senior Notes

Due 2019

TABLE OF CONTENTS*

i

THIS FIFTH SUPPLEMENTAL INDENTURE is made as of September 22, 2009, by and between MARKEL CORPORATION, a Virginia corporation, having its principal office at 4521 Highwoods Parkway, Glen Allen, Virginia 23060 (the “Company”), and THE BANK OF NEW YORK MELLON (as successor to THE CHASE MANHATTAN BANK), a New York banking corporation, as Trustee (herein called the “Trustee”).

W I T N E S S E T H:

WHEREAS, the Company has heretofore entered into a Senior Indenture, dated as of June 5, 2001 (the “Original Indenture”), as heretofore supplemented and amended, with the Trustee;

WHEREAS, the Original Indenture is incorporated herein by this reference and the Original Indenture, as heretofore supplemented and amended and as further supplemented by this Fifth Supplemental Indenture, is herein called the “Indenture”;

WHEREAS, under the Original Indenture, a new series of Securities may at any time be established in accordance with the provisions of the Original Indenture and the terms of such series may be described by a supplemental indenture executed by the Company and the Trustee;

WHEREAS, the Company proposes to create under the Indenture a series of Securities;

WHEREAS, additional Securities of other series hereafter established, except as may be limited in the Original Indenture as at the time supplemented and modified, may be issued from time to time pursuant to the Indenture as at the time supplemented and modified; and

WHEREAS, all conditions necessary to authorize the execution and delivery of this Fifth Supplemental Indenture and to make it a valid and binding obligation of the Company have been done or performed.

NOW, THEREFORE, in consideration of the agreements and obligations set forth herein and for other good and valuable consideration, the sufficiency of which is hereby acknowledged, the parties hereto hereby agree as follows:

ARTICLE I

7.125% SENIOR NOTES DUE 2019

SECTION 101. Establishment . There is hereby established a new series of Securities to be issued under the Indenture, to be designated as the Company’s 7.125% Senior Notes due 2019 (the “7.125% Senior Notes”).

There are to be authenticated and delivered $350,000,000 principal amount of 7.125% Senior Notes, and such principal amount of the 7.125% Senior Notes may be increased from time to time pursuant to Section 301 of the Indenture. All 7.125% Senior Notes need not be issued at the same time and such series may be reopened at any time, without the consent of any Holder, for issuances of additional 7.125% Senior Notes. Any such additional 7.125% Senior Notes will have the same interest rate, maturity and other terms as those initially issued. Further 7.125% Senior Notes may also be authenticated and delivered as provided by Sections 304, 305, 306 or 905 of the Original Indenture.

The 7.125% Senior Notes shall be issued in definitive fully registered form without coupons, in substantially the form set out in Exhibit A hereto. The entire initially issued principal amount of the 7.125% Senior Notes shall initially be evidenced by one or more certificates issued to Cede & Co., as nominee for The Depository Trust Company.

The form of the Trustee’s Certificate of Authentication for the 7.125% Senior Notes shall be in substantially the form set forth in Exhibit B hereto.

Each 7.125% Senior Note shall be dated the date of authentication thereof and shall bear interest from the Original Issue Date or from the most recent Interest Payment Date to which interest has been paid or duly provided for.

SECTION 102. Definitions . The following defined terms used herein shall, unless the context otherwise requires, have the meanings specified below. Capitalized terms used herein for which no definition is provided herein shall have the meanings set forth in the Original Indenture.

“Business Day” means a day other than (i) a Saturday or a Sunday, (ii) a day on which banks in New York, New York are authorized or obligated by law or executive order to remain closed or (iii) a day on which the Corporate Trust Office is closed for business.

“Comparable Treasury Issue” means the United States Treasury security selected by a Reference Treasury Dealer as having an actual or interpolated maturity comparable to the remaining term of the 7.125% Senior Notes called for redemption, that would be utilized, at the time of selection and in accordance with customary financial practice, in pricing new issues of corporate debt securities of comparable maturity to the remaining term of 7.125% Senior Notes called for redemption.

“Comparable Treasury Price” means, with respect to any Redemption Date, the average, as determined by the Company, of the Reference Treasury Dealer Quotations for that Redemption Date.

“Corporate Trust Office” means the office of the Trustee at which at any particular time its corporate trust business shall be principally administered in the Borough of Manhattan, The City of New York, which office at the date of original execution of this Indenture is located at 101 Barclay Street 8 W, New York, New York 10286.

“Interest Payment Dates” means March 30 and September 30 of each year, commencing on March 30, 2010.

“Lien” means any mortgage, lien, pledge, security interest or other encumbrance of any kind.

2

“Material Subsidiary” means a Subsidiary of the Company whose total assets (as determined in accordance with GAAP) represent at least 20% of the total assets of the Company on a consolidated basis.

“Original Issue Date” means September 22, 2009.

“Outstanding”, when used with respect to the 7.125% Senior Notes, means, as of the date of determination, all 7.125% Senior Notes, theretofore authenticated and delivered under the Indenture, except:

(i) 7.125% Senior Notes theretofore canceled by the Trustee or delivered to the Trustee for cancellation;

(ii) 7.125% Senior Notes for whose payment at Maturity the necessary amount of money or money’s worth has been theretofore deposited (other than pursuant to Section 402 of the Original Indenture) with the Trustee or any Paying Agent (other than the Company) in trust or set aside and segregated in trust by the Company (if the Company shall act as its own Paying Agent) for the Holders of such 7.125% Senior Notes.

(iii) 7.125% Senior Notes with respect to which the Company has effected defeasance, or covenant defeasance has been effected, pursuant to Section 402 of the Original Indenture; and

(iv) 7.125% Senior Notes that have been paid pursuant to Section 306 of the Original Indenture or in exchange for or in lieu of which other 7.125% Senior Notes have been authenticated and delivered pursuant to the Indenture, other than any such 7.125% Senior Notes in respect of which there shall have been presented to the Trustee proof satisfactory to it that such 7.125% Senior Notes are held by a bona fide purchaser in whose hands such 7.125% Senior Notes are valid obligations of the Company; provided, however, that in determining whether the Holders of the requisite principal amount of Outstanding 7.125% Senior Notes have given any request, demand, authorization, direction, notice, consent or waiver hereunder or are present at a meeting of Holders of 7.125% Senior Notes for quorum purposes, 7.125% Senior Notes owned by the Company or any other obligor upon the 7.125% Senior Notes or any Affiliate of the Company or such other obligor shall be disregarded and deemed not to be Outstanding, except that, in determining whether the Trustee shall be protected in making any such determination or relying upon any such request, demand, authorization, direction, notice, consent or waiver, only 7.125% Senior Notes which a Responsible Officer of the Trustee knows to be so owned shall be so disregarded. 7.125% Senior Notes so owned which shall have been pledged in good faith may be regarded as Outstanding if the pledgee establishes to the satisfaction of the Trustee (A) the pledgee’s right so to act with respect to such 7.125% Senior Notes and (B) that the pledgee is not the Company or any other obligor upon the 7.125% Senior Notes or an Affiliate of the Company or such other obligor.

“Reference Treasury Dealer” means Wells Fargo Securities, LLC and Barclays Capital Inc. and one other U.S. Government securities dealer selected by the Company, and each of their respective successors.

3

“Reference Treasury Dealer Quotations” means, on any redemption date, the average, as determined by the Company, of the bid and asked prices for the Comparable Treasury Issue (expressed in each case as a percentage of its principal amount) quoted in writing to the Company by each Reference Treasury Dealer at 3:30 p.m., New York City time, on the third business day preceding that Redemption Date.

“Regular Record Date” means, with respect to each Interest Payment Date, the close of business on the Business Day preceding such Interest Payment Date; provided, that with respect to 7.125% Senior Notes that are not represented by one or more Global Securities, the Regular Record Date shall be the close of business on the 15th calendar day (whether or not a Business Day) preceding such Interest Payment Date.

“Remaining Scheduled Payments” means the remaining scheduled payments of principal of and interest on the 7.125% Senior Notes called for redemption that would be due after the related Redemption Date but for that redemption. If that Redemption Date is not an interest payment date with respect to the 7.125% Senior Notes called for redemption, the amount of the next succeeding scheduled interest payment on such 7.125% Senior Notes will be reduced by the amount of interest accrued to such Redemption Date.

“Stated Maturity” means September 30, 2019.

“Treasury Rate” means, with respect to any Redemption Date, the rate per year equal to the semi-annual equivalent yield to maturity (computed as of the third business day immediately preceding that Redemption Date) of the Comparable Treasury Issue, assuming a price for the Comparable Treasury Issue (expressed as a percentage of its principal amount) equal to the Comparable Treasury Price for that Redemption Date.

SECTION 103. Payment of Principal and Interest . The principal of the 7.125% Senior Notes shall be due at the Stated Maturity. The unpaid principal amount of the 7.125% Senior Notes shall bear interest at the rate of 7.125% per annum until paid or duly provided for, such interest to accrue from the Original Issue Date or from the most recent Interest Payment Date to which interest has been paid or duly provided for. Interest shall be paid semiannually in arrears on each Interest Payment Date to the Person in whose name the 7.125% Senior Notes are registered on the Regular Record Date for such Interest Payment Date; provided that interest payable at the Stated Maturity of principal as provided herein will be paid to the Person to whom principal is payable. Any such interest that is not so punctually paid or duly provided for will forthwith cease to be payable to the Holders on such Regular Record Date and may either be paid to the Person or Persons in whose name the 7.125% Senior Notes are registered at the close of business on a Special Record Date for the payment of such defaulted interest to be fixed by the Trustee (in accordance with Section 307 of the Original Indenture), notice whereof shall be given to Holders of the 7.125% Senior Notes not less than ten (10) days prior to such Special Record Date, or be paid at any time in any other lawful manner not inconsistent with the requirements of any securities exchange, if any, on which the 7.125% Senior Notes may be listed, and upon such notice as may be required by any such exchange, all as more fully provided in the Original Indenture.

4

Payments of interest on the 7.125% Senior Notes will include interest accrued to but excluding the respective Interest Payment Dates. Interest payments for the 7.125% Senior Notes shall be computed and paid on the basis of a 360-day year of twelve 30-day months. In the event that any date on which interest is payable on the 7.125% Senior Notes is not a Business Day, then payment of the interest payable on such date will be made on the next succeeding day that is a Business Day (and without any interest or payment in respect of any such delay), in each case with the same force and effect as if made on the date the payment was originally payable.

Payment of the principal and interest on the 7.125% Senior Notes shall be made at the office of the Paying Agent in such coin or currency of the United States of America as at the time of payment is legal tender for payment of public and private debts, with any such payment that is due at the Stated Maturity of any 7.125% Senior Notes being made upon surrender of such 7.125% Senior Notes to the Paying Agent. Payments of interest (including interest on any Interest Payment Date) will be made, subject to such surrender where applicable, at the option of the Company, (i) by check mailed to the address of the Person entitled thereto as such address shall appear in the Security Register or (ii) by wire transfer at such place and to such account at a banking institution in the United States as may be designated in writing to the Trustee at least sixteen (16) days prior to the date for payment by the Person entitled thereto. In the event that any date on which principal and interest is payable on the 7.125% Senior Notes is not a Business Day, then payment of the principal and interest payable on such date will be made on the next succeeding day that is a Business Day (and without any interest or payment in respect of any such delay), in each case with the same force and effect as if made on the date the payment was originally payable.

SECTION 104. Denominations . The 7.125% Senior Notes may be issued in denominations of $1,000, or any integral multiple thereof.

SECTION 105. Global Securities . The 7.125% Senior Notes will be issued initially in the form of one or more Global Securities registered in the name of the Depositary (which shall be The Depository Trust Company) or its nominee. Except under the limited circumstances described below, 7.125% Senior Notes represented by such Global Securities will not be exchangeable for, and will not otherwise be issuable as, 7.125% Senior Notes in definitive form. The Global Securities described above may not be transferred except by the Depositary to a nominee of the Depositary or by a nominee of the Depositary to the Depositary or another nominee of the Depositary or to a successor Depositary or its nominee.

Owners of beneficial interests in such a Global Security will not be considered the Holders thereof for any purpose under the Indenture, and no Global Security representing a 7.125% Senior Note shall be exchangeable, except for another Global Security of like denomination and tenor to be registered in the name of the Depositary or its nominee or to a successor Depositary or its nominee or except as described below. The rights of Holders of such Global Security shall be exercised only through the Depositary.

A Global Security shall be exchangeable for 7.125% Senior Notes registered in the names of persons other than the Depositary or its nominee only if (i) the Depositary notifies the Company that it is unwilling or unable to continue as a Depositary for such Global Security and

5

no successor Depositary shall have been appointed by the Company within 90 days of receipt by the Company of such notification, or if at any time the Depositary ceases to be a clearing agency registered under the Exchange Act at a time when the Depositary is required to be so registered to act as such Depositary and no successor Depositary shall have been appointed by the Company within 90 days after it becomes aware of such cessation, or (ii) the Company in its sole discretion determines that such Global Security shall be so exchangeable. Any Global Security that is exchangeable pursuant to the preceding sentence shall be exchangeable for 7.125% Senior Notes registered in such names as the Depositary shall direct.

SECTION 106. Redemption . The 7.125% Senior Notes are redeemable, as a whole or in part, at the Company’s option, at any time or from time to time, upon notice mailed to the registered address of each Holder at least 30 days but not more than 60 days prior to the Redemption Date. The Redemption Price will be equal to the greater of (1) 100% of the principal amount of the 7.125% Senior Notes to be redeemed and (2) the sum of the present values of the Remaining Scheduled Payments on such 7.125% Senior Notes discounted to the Redemption Date, on a semi-annual basis (assuming a 360-day year consisting of twelve 30-day months), at a rate equal to the sum of the applicable Treasury Rate plus 50 basis points. Accrued interest will be paid to, but excluding, the Redemption Date.

On and after a Redemption Date, interest will cease to accrue on the 7.125% Senior Notes called for redemption (unless the Company defaults in the payment of the Redemption Price and accrued interest). On or before a Redemption Date, the Company shall deposit with the Paying Agent or the Trustee money sufficient to pay the Redemption Price of and accru