Exhibit 10.1

SUPPLEMENTAL LETTER

      To:  
Alterra Capital UK Limited
(formerly named Max UK Holdings Ltd.)
70 Gracechurch Street
London EC3V 0XL
(the “Account Party” and the “Applicant”)
   
Alterra Capital Holdings Limited
(formerly named Max Capital Group Ltd.)
Alterra House, 2 Front Street
Hamilton, Bermuda
(the “Guarantor”)

Alterra Corporate Capital 2 Limited

(formerly named Max Corporate Capital 2 Limited., Danish Re Capital Limited and
Imagine Corporate Capital 2 Limited)

70 Gracechurch Street

London EC3V 0XL

(“Alterra Corporate 2”)

Alterra Corporate Capital 3 Limited

(formerly named Max Corporate Capital 3 Limited)

70 Gracechurch Street

London EC3V 0XL

(together with Alterra Corporate 2, the “Corporate Members”)

19 December 2011

Dear Sirs

£60,000,000 Letter of Credit Facility Agreement dated 13 October 2008 (as
amended and restated on 30 March 2010, as amended by a supplemental letter dated
26 November 2010 and as further amended and restated on 16 December 2010)

This letter is addressed to you in connection with the £60,000,000 credit
facility agreement (the "Credit Facility Agreement”) dated 13 October 2008 (as
amended and restated on 30 March 2010, as amended by a supplemental letter dated
26 November 2010 and as further amended and restated on 16 December 2010)
entered into between (1) the Guarantor, (2) the Account Party and the Applicant
and (3) ourselves in our separate capacities as Bank, Agent, Issuing Bank and
Security Trustee.

    Terms defined in the Credit Facility Agreement shall have the same meanings
in this letter.

WHEREAS:

(A)   The Account Party has requested that (i) the expiry date of the Commitment
Period and (ii) the date by which the Issuing Bank may give notice of
termination of a Letter of Credit in accordance with the terms of the Letter of
Credit both be extended.

(B)   The parties wish to amend the Credit Facility Agreement on the terms set
out in this letter.

    NOW IT IS AGREED:

1.   In consideration of the Account Party and the Applicant, the Guarantor and
each Corporate Member continuing to perform their obligations under the Credit
Facility Agreement and the other Finance Documents and subject to receiving
(i) an original of this letter signed by each of the Account Party, the
Applicant, the Guarantor and each Corporate Member acknowledging and consenting
to its terms and (ii) such documents or evidence as the Agent may require
evidencing approval and authorising the execution of this letter, we consent to
the extension of (i) the expiry date of the Commitment Period and (ii) the date
by which the Issuing Bank may give notice of termination of a Letter of Credit
in accordance with the terms of the Letter of Credit. .

2.   Subject to Clause 1, the Credit Facility Agreement shall, with effect on
and from the date of this letter, be (and it is hereby) amended and varied as
follows:

  (a)   The definition of “Commitment Period” shall be deleted in its entirety
and replaced with the following:

"Commitment Period” means the period commencing on the date of this Agreement
and ending on the earlier of (a) 30 June 2012 and (b) the date on which the
Commitments of the Banks are cancelled in accordance with any applicable
provision of this Agreement;”; and

  (b)   Clause 3.11 shall be deleted in its entirety and replaced with the
following:

“The Issuing Bank may, in its absolute discretion, at any time up to and
including 30 June 2012, serve notice on Lloyd’s giving 4 years notice of
termination of a Letter of Credit, in accordance with the terms of the Letter of
Credit.”

3.   The rights and obligations of the parties under the Credit Facility
Agreement and the other Finance Documents shall continue in full force and
effect, uninterrupted by the amendments under this letter save insofar as they
are amended hereby and the Security Interests created by the relevant Finance
Documents shall continue fully to secure the obligations of the Account Party
under the Credit Facility Agreement as so amended.

4.   Any transfer or assignment made in accordance with the terms of the Credit
Facility Agreement shall have the same effect in relation to the rights and
obligations of the parties under this letter as it has in relation to their
rights and obligations under the Credit Facility Agreement.

5.   The provisions of clauses 1.4 (Rights of third parties), 16.3 (Indemnity
against costs), 26 (Assignments and Transfers), 28 (Miscellaneous), 30 (Notices)
and 31 (Applicable Law and Jurisdiction) of the Credit Facility Agreement shall
be incorporated into this letter as if set out herein and as if references
therein to “this Agreement” were references to this letter and as though this
letter were included in the definition of “Finance Documents”.

Please acknowledge your consent to and agreement of the foregoing by signing and
returning to us a copy of this letter.

Yours faithfully

...................................................
ING BANK N.V., LONDON BRANCH

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Agreed and accepted this 19th day of December 2011

...................................................
For and on behalf of
ALTERRA CAPITAL UK LIMITED

...................................................
For and on behalf of
ALTERRA CAPITAL HOLDINGS LIMITED

...................................................
For and on behalf of
ALTERRA CORPORATE CAPITAL 2 LIMITED

...................................................
For and on behalf of
ALTERRA CORPORATE CAPITAL 3 LIMITED

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