Document:

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                                                                    EXHIBIT 10.9

                                                                           FINAL

                                 Amendment No. 4
                                       to
                              Procurement Agreement

This Amendment ("Amendment") is made and entered into effective this 23rd day of
April, 2001, by and between WILLIAMS COMMUNICATIONS, LLC ("Williams") and CORVIS
CORPORATION ("Corvis").

                                  -WITNESSETH-

WHEREAS, Williams and Corvis are parties to that certain Procurement Agreement
which is dated April 6, 2000, and which has been subsequently amended by
amendments dated May 3, 2000, June 23, 2000 and January 9, 2001 (the
"Agreement"); and

WHEREAS, Williams and Corvis desire to further amend the Agreement.

NOW, THEREFORE in consideration of the foregoing premises and mutual promises
and covenants of the parties hereto, the receipt and sufficiency of which is
hereby acknowledged, Williams and Corvis agree to amend the Agreement as
follows:

1.   Attachment 3.2 is hereby deleted in its entirety and Attachment 3.2
(Revised), attached hereto and made a part hereof by this reference, is inserted
in substitution thereof.

2.   Unless specifically indicated otherwise, all capitalized terms used herein
shall have the same meaning given to them in the Agreement

3.   Except as specifically amended herein, all terms, conditions and provisions
contained in the Agreement shall remain unchanged and in full force and effect.

IN WITNESS WHEREOF, the parties have executed this Amendment on the day and year
first above set forth.

WILLIAMS COMMUNICATIONS, LLC                          CORVIS CORPORATION

____________________________                          _________________________
         (SIGNATURE)                                         (SIGNATURE)

____________________________                          _________________________
         (PRINT)                                             (PRINT)

____________________________                          _________________________
         (TITLE)                                             (TITLE)

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                                                        Attachment 3.2 (Revised)

         For Corvis Equipment purchased pursuant to Sections 3.2(a)(i) and
3.2(a)(ii) of this Agreement (excluding any Field Trial Equipment), the normal
payment terms of the Agreement shall be modified as follows:

         Corvis shall invoice Customer upon shipment for only [*] % of the
purchase price for Corvis optical network gateway common equipment, optical
amplifiers, and optical add/drop multiplexers ("Corvis Common Equipment").
Corvis Common Equipment shall not include transmitters or receivers. The
remaining purchase price will be due and payable (net 30 days) as follows:

                    .  [*] % of the unpaid portion of the purchase price of the
                       Corvis Common Equipment to be deployed on a particular
                       Span (as defined below) upon the earliest to occur of (i)
                       utilization of [*] % of the transmission capacity (as
                       defined below) on (or at either end of) the particular
                       Span on which the Corvis Common Equipment is deployed; or
                       (ii) [*] months after shipment of the Corvis Common
                       Equipment.

                    .  The remaining unpaid balance of the purchase price of the
                       Corvis Common Equipment to be deployed on a particular
                       Span upon the earliest to occur of (i) utilization of [*]
                       % of the transmission capacity (as defined below) on (or
                       at either end of) the particular Span on which the Corvis
                       Common Equipment is deployed, or (ii) [*] months after
                       shipment of the Corvis Common Equipment.

         As used in this Attachment 3.2, "Span" means the service-carrying
sections of a network which are bounded by line terminating elements. For the
route from [*] to [*], the Spans are: [*] to [*]; [*] to [*]; [*] to [*]; [*] to
[*]; [*] to [*]; [*] to [*].

         As used in this Attachment 3.2, "[*] % of the transmission capacity"
for the [*] to [*] route equals [*], and for the [*] to [*] route equals [*].
Further, as used in this Attachment 3.2, "[*] % of the transmission capacity"
for the [*] to [*] route equals [*], and for the [*] to [*] route equals [*].

         Utilization will be determined at true-up meetings and additional
payments will be payable immediately based on utilization thresholds mentioned
above. If additional payments are due based upon elapse of time as opposed to
utilization, such payments are to be made immediately upon the lapse of the
relevant time. Corvis reserves the right to audit utilization.

         Initial order and "Standard Term Tx/Rx Cards" ordered are subject to
normal invoicing and payment terms as provided in this Agreement.  For each
"Standard Term

[*] Confidential treatment requested.

                                        2

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Tx/Rx Card" order, Williams may order an additional quantity of "Build Ahead
Tx/Rx Cards" to be used for pre-provisioning (not to exceed the Build Ahead
Limit, defined below) to be shipped and installed in the network span. The
"Build Ahead Limit" means, in any calendar quarter, the quantity and delivery
schedule of Tx/Rx Cards specified in Williams' reasonable Rolling Forecast for
such quarter. The parties shall meet at the beginning of each quarter to review
and adjust the Build Ahead Limit for the quarter; provided, that in no event
shall the Build Ahead Limit exceed [*] TxRx Cards without Corvis' prior consent.
The Build Ahead Tx/Rx Cards will be separately invoiced at shipment on net [*]
Day payment terms and must be either paid for or returned by such date. A TxRx
Group is a set of sixteen TxRx Cards ordered as a set, identifiable by serial
number. If any Build Ahead Tx/Rx Card pair within a TxRx Group is utilized,
payment for all build-ahead pairs in the TxRx Group will be immediately due.

      All orders are subject to the agreed upon volume forecasting process.

[*] Confidential treatment requested.

                                       3<PAGE>
                                                                   Exhibit 10.10

                                 AMENDMENT NO. 6

THIS AMENDMENT NO. 6 ("Amendment") is made and entered into effective this 25th
day of September, 2001, by and between WILLIAMS COMMUNICATIONS, LLC ("Customer")
and CORVIS CORPORATION ("Corvis").

WHEREAS, Customer and Corvis are parties to that certain Procurement Agreement
dated April 6, 2000, which has been subsequently amended from time to time (the
"Agreement"); and

WHEREAS, Customer and Corvis desire to further amend the Agreement; and

NOW, THEREFORE in consideration of the foregoing premises and mutual promises
and covenants of the parties hereto, the receipt and sufficiency of which is
hereby acknowledged, Customer and Corvis agree to amend the Agreement as
follows:

1.   The following language shall be added to the end of Attachment 3.2
(Revised), provided for by Amendment No. 4, dated April 23, 2001, to the
Procurement Agreement:

          In connection solely with the Corvis Products to be sold to Customer
     from time to time under the Agreement, which are also financed by Corvis or
     with respect to which Corvis had provided deferred payment terms to
     Customer (the "Financed Products"), and in consideration for the extension
     of payment terms and other valuable consideration, Corvis reserves, and
     Customer hereby grants to Corvis, a purchase money security interest in any
     Financed Products sold to Customer by Corvis under or pursuant to this
     Agreement until any and all payments, charges and other amounts due or to
     become due to Corvis solely for the purchase of such Financed Products,
     including without limitation taxes, and shipping and installation charges
     for the Financed Products, are paid in full.

          Corvis shall have the right and is hereby authorized, at any time and
     without notice to Customer, to file in any state or local jurisdiction, and
     Customer hereby agrees to execute upon request from Corvis, such financing
     statements (e.g., UCC-1 financing statements) or other writings as Corvis
     reasonably from time to time deems necessary to perfect and continue the
     perfection of the purchase money security interest granted hereunder.
     Notwithstanding the foregoing, Customer hereby appoints Corvis as its
     attorney-in-fact for the sole purpose of the above said filing and, to the
     extent necessary, to execute any such financing statements and such other
     writings prepared by Corvis or its designee solely for purposes of
     perfecting or maintaining the perfection of Corvis' purchase money security
     interest granted hereunder. Customer also agrees that this Amendment, or a
     carbon, xerographic or other copy hereof may be filed by Corvis in any
     state or local jurisdiction as a financing statement (or as other evidence
     of Corvis' purchase money security interest). Customer shall not sell or
     lease the Financed Products or allow any liens or encumbrances to attach to
     the

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     Financed Products without written permission of Corvis prior to payment in
     full for the Financed Products.

          In addition to any other remedy available to Corvis as provided
     herein, by common law or by statute, Corvis may, if applicable, exercise
     its rights pursuant to UCC 2-702 or such other applicable provision as may
     exist from state to state.

2.   Except as specifically amended herein, all other provisions of the
Agreement shall remain unchanged and in full force and effect.

IN WITNESS WHEREOF, the parties have executed this Amendment as of the day and
year last set forth below.

WILLIAMS COMMUNICATIONS, LLC                  CORVIS CORPORATION

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         (SIGNATURE)                              (SIGNATURE)

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         (PRINT)                                  (PRINT)

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         (TITLE)                                  (TITLE)

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         (DATE)                                   (DATE)

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