EXHIBIT 99.1

ALTERRA CAPITAL REPORTS FOURTH QUARTER AND YEAR END 2012 RESULTS

Fourth Quarter Net Operating Loss of $0.52 per Diluted Share

2012 Net Operating Income of $1.18 per Diluted Share

2012 Diluted Book Value per Share Growth of 7.5%, including Dividends

HAMILTON, BERMUDA, February 5, 2013—Alterra Capital Holdings Limited (NASDAQ: ALTE; BSX: ALTE.BH) (“Alterra”) today reported a net loss of $51.8 million, or a loss of $0.54 per diluted share, for the fourth quarter of 2012, compared to net income of $30.9 million, or $0.30 per diluted share, for the same quarter of 2011.

The net operating loss for the fourth quarter of 2012 was $49.7 million, or a loss of $0.52 per diluted share, compared to net operating income of $31.7 million, or $0.30 per diluted share, for the same quarter of 2011.

For the year ended December 31, 2012, Alterra reported net income of $143.8 million, or $1.43 per diluted share, compared to net income of $65.3 million, or $0.61 per diluted share, for the year ended December 31, 2011. Net operating income for the year ended December 31, 2012 was $119.1 million, or $1.18 per diluted share, compared to net operating income of $96.6 million, or $0.91 per diluted share, for the year ended December 31, 2011. Net operating return on average shareholders’ equity for the year ended December 31, 2012 was 4.2%.

W. Marston (Marty) Becker, President and Chief Executive Officer of Alterra, said: “Alterra’s fourth quarter operating results were impacted heavily by Hurricane Sandy. However, for the year, we are pleased to report net income of $143.8 million and growth in diluted book value per share of 7.5%, including dividends. Our 2012 results reflect the diversified underwriting strategy and risk management discipline that has served us well, particularly in years with major industry losses such as Sandy.

“On December 19 we ended the year with the announcement of a merger agreement pursuant to which Alterra will be acquired by Markel Corporation. The transaction is subject to shareholder and regulatory approval and is expected to close in the first half of 2013. We believe the combined company will establish itself as a leading specialty insurance and reinsurance company with greater capacity and a broader range of products and services, and will be better positioned for long-term success, including the creation of superior shareholder value,” Mr. Becker concluded.

Fourth quarter 2012 results for Alterra include:

Gross premiums written and net premiums written from property and casualty underwriting for the fourth quarter of 2012 are shown in the following table, with the increase/decrease compared to the same quarter of 2011:

Results for the year ended December 31, 2012 include:

Gross premiums written and net premiums written from property and casualty underwriting for the year ended December 31, 2012 are shown in the following table, with the increase/decrease compared to the same period of 2011:

Balance Sheet

Total invested assets, including cash and cash equivalents, were $8,032.6 million as of December 31, 2012, an increase of $217.9 million from December 31, 2011. As of December 31, 2012, 95.9% of the fixed maturities portfolio (by carrying value) was investment-grade, an increase from 94.4% as of December 31, 2011. As of December 31, 2012, the weighted average book yield of Alterra’s cash and fixed maturities portfolio was 3.15%, and the weighted average duration was 4.5 years.

Share repurchases under the Board-approved share repurchase authorization for the year ended December 31, 2012 were 6,626,684 common shares at an average price of $23.03 per share for a total of $152.6 million. Alterra did not repurchase any common shares under the share repurchase authorization during the fourth quarter of 2012. As of December 31, 2012, $301.7 million remained under the share repurchase authorization.

Shareholders’ equity was $2,839.7 million as of December 31, 2012, an increase of 1.1% from December 31, 2011. Diluted book value per share as of December 31, 2012 was $28.34. Including dividends declared, diluted book value per share decreased for the fourth quarter of 2012 by 3.6%, and grew by 7.5% for the year ended December 31, 2012. Not included in shareholders’ equity as of December 31, 2012 were $218.0 million of unrecognized gains on held-to-maturity securities, which represented $2.18 in unrecognized diluted book value per share.

A copy of Alterra’s fourth quarter financial supplement is available on Alterra’s website at www.alterracap.com.

Alterra Capital Holdings Limited is a global enterprise dedicated to providing diversified specialty insurance and reinsurance products to corporations, public entities and property and casualty insurers.

Non-GAAP Financial Measures

In presenting Alterra’s results, management has included and discussed net operating income, net operating income per diluted share, annualized net operating return on average shareholders’ equity, net operating return on average shareholders’ equity and diluted tangible book value per share. These measures are “non-GAAP financial measures” as defined in Regulation G. Management believes that these non-GAAP financial measures, which may be defined differently by other companies, allow for a more complete understanding of Alterra’s business. These measures, however, should not be viewed as a substitute for measures determined in accordance with U.S. GAAP. The reconciliation of these measures to their respective most directly comparable U.S. GAAP financial measures is presented in the attached financial information in accordance with Regulation G.

INFORMATION CONCERNING FORWARD-LOOKING STATEMENTS

This release includes statements about future economic performance, finances, expectations, plans and prospects of Alterra and Markel, both individually and on a combined basis, that are forward-looking statements for purposes of the safe harbor provisions of the Private Securities Litigation Reform Act of 1995. There are risks and uncertainties that could cause actual results to differ materially from those expressed in or suggested by such statements. For further information regarding factors affecting future results of Alterra and Markel, please refer to their respective Annual Report on Form 10-K for the year ended December 31, 2011 and Quarterly Reports on Form 10-Q and other documents filed by Alterra and Markel since March 1, 2012 with the Securities Exchange Commission (“SEC”). These documents are also available free of charge, in the case of Alterra, by directing a request to Alterra through Joe Roberts, Chief Financial Officer, or Susan Spivak Bernstein, Senior Vice President, Investor Relations, at 441-295-8800 and, in the case of Markel, by directing a request to Bruce Kay, Investor Relations, at 804-747-0136. Neither Alterra nor Markel undertakes any obligation to update or revise publicly any forward-looking statement whether as a result of new information, future developments or otherwise.

This release contains certain forward-looking statements within the meaning of the U.S. federal securities laws. Statements that are not historical facts, including statements about Alterra’s and Markel’s beliefs, plans or expectations, are forward-looking statements. These statements are based on Alterra’s or Markel’s current plans, estimates and expectations. Some forward-looking statements may be identified by use of terms such as “believe,” “anticipate,” “intend,” “expect,” “project,” “plan,” “may,” “should,” “could,” “will,” “estimate,” “predict,” “potential,” “continue,” and similar words, terms or statements of a future or forward-looking nature. In light of the inherent risks and uncertainties in all forward-looking statements, the inclusion of such statements in this release should not be considered as a representation by Alterra, Markel or any other person that Alterra’s or Markel’s objectives or plans, both individually and on a combined basis, will be achieved. A non-exclusive list of important factors that could cause actual results to differ materially from those in such forward-looking statements includes the following: (a) the occurrence of natural or man-made catastrophic events with a frequency or severity exceeding expectations; (b) the adequacy of loss reserves and the need to adjust such reserves as claims develop over time; (c) the failure of any of the loss limitation methods the parties employ; (d) any adverse change in financial ratings of either company or their subsidiaries; (e) the effect of competition on market trends and pricing; (f) cyclical trends, including with respect to demand and pricing in the insurance and reinsurance markets; (g) changes in general economic conditions, including changes in interest rates and/or equity values in the United States of America and elsewhere; and (h) other factors set forth in Alterra’s and Markel’s recent reports on Form 10-K, Form 10-Q and other documents filed with the SEC by Alterra and Markel.

* * * * *

Risks and uncertainties relating to the proposed transaction include the risks that: (1) the parties will not obtain the requisite shareholder or regulatory approvals for the transaction; (2) the anticipated benefits of the transaction will not be realized or the parties may experience difficulties in successfully integrating the two companies; (3) the parties may not be able to retain key personnel; (4) the conditions to the closing of the proposed merger may not be satisfied or waived; (5) the outcome of any legal proceedings to the extent initiated against Alterra or Markel or its respective directors and officers following the announcement of the proposed merger is uncertain; (6) the acquisition may involve unexpected costs; and (7) the businesses may suffer as a result of uncertainty surrounding the acquisition. These risks, as well as other risks of the combined company and its subsidiaries may be different from what the companies expect, or have previously experienced, and each party’s management may respond differently to any of the aforementioned factors. These risks, as well as other risks associated with the merger, are more fully discussed in the joint proxy statement/prospectus of Markel and Alterra that has been filed with the SEC. Readers are cautioned not to place undue reliance on any forward-looking statements, which speak only as of the date on which they are made.

ADDITIONAL INFORMATION ABOUT THE PROPOSED MERGER AND WHERE TO FIND IT:

This release relates to a proposed merger between Alterra and Markel. On December 27, 2012, Markel filed with the SEC a registration statement on Form S-4, and on January 18, 2013, Markel and Alterra each filed the definitive joint proxy statement/prospectus. This release is not a substitute for the definitive joint proxy statement/prospectus or any other document that Markel or Alterra filed or may file with the SEC or send to its shareholders in connection with the proposed merger. INVESTORS AND SECURITY HOLDERS ARE URGED TO READ THE DEFINITIVE JOINT PROXY STATEMENT/PROSPECTUS AND ALL OTHER RELEVANT DOCUMENTS FILED OR THAT MAY BE FILED WITH THE SEC OR SENT TO SHAREHOLDERS AS THEY BECOME AVAILABLE BECAUSE THEY CONTAIN OR WILL CONTAIN IMPORTANT INFORMATION ABOUT THE PROPOSED MERGER. All documents, when filed, will be available free of charge at the SEC’s website (www.sec.gov) or, in the case of Alterra, by directing a request to Joe Roberts, Chief Financial Officer, or Susan Spivak Bernstein, Senior Vice President, Investor Relations, at 441-295-8800 and, in the case of Markel, by directing a request to Bruce Kay, Investor Relations, at 804-747-0136.

PARTICIPANTS IN THE SOLICITATION:

Alterra and Markel and their respective directors and executive officers may be deemed to be participants in any solicitation of proxies from both Alterra’s and Markel’s shareholders in favor of the proposed transaction. Information about Alterra’s directors and executive officers and their ownership in Alterra common stock is available in the proxy statement dated March 26, 2012 for Alterra’s 2012 annual general meeting of shareholders. Information about Markel’s directors and executive officers and their ownership of Markel common stock is available in the proxy statement dated March 16, 2012 for Markel’s 2012 annual meeting of shareholders.

ALTERRA CAPITAL HOLDINGS LIMITED

CONSOLIDATED BALANCE SHEETS

(Expressed in thousands of United States Dollars, except per share and share amounts)

ALTERRA CAPITAL HOLDINGS LIMITED

CONSOLIDATED STATEMENTS OF OPERATIONS AND COMPREHENSIVE INCOME (Unaudited)

(Expressed in thousands of United States Dollars, except per share and share amounts)

ALTERRA CAPITAL HOLDINGS LIMITED

CONSOLIDATED STATEMENTS OF CHANGES IN SHAREHOLDERS’ EQUITY (Unaudited)

(Expressed in thousands of United States Dollars)

ALTERRA CAPITAL HOLDINGS LIMITED

CONSOLIDATED STATEMENTS OF CASHFLOWS (Unaudited)

(Expressed in thousands of United States Dollars)

SUPPLEMENTAL DISCLOSURES OF CASH FLOW INFORMATION

Interest paid totaled $28,400 and $28,582 for the years ended December 31, 2012 and 2011, respectively.

Income taxes paid totaled $7,954 and $2,049 for the years ended December 31, 2012 and 2011, respectively.

ALTERRA CAPITAL HOLDINGS LIMITED

SCHEDULE OF SUPPLEMENTAL SEGMENT DATA—THREE MONTHS ENDED DECEMBER 31, 2012 (Unaudited)

(Expressed in thousands of United States Dollars)

SCHEDULE OF SUPPLEMENTAL SEGMENT DATA—YEAR ENDED DECEMBER 31, 2012 (Unaudited)

(Expressed in thousands of United States Dollars)