SQL> select * from v$version;

BANNER
----------------------------------------------------------------
Oracle Database 10g Enterprise Edition Release 10.2.0.2.0 - 64bi
PL/SQL Release 10.2.0.2.0 - Production
CORE    10.2.0.2.0      Production
TNS for HPUX: Version 10.2.0.2.0 - Production
NLSRTL Version 10.2.0.2.0 - Production

SQL> drop table mytable purge;

Table dropped.

SQL> create table mytable as select * from cat;

Table created.

SQL> create index mytable_idx on mytable(table_type);

Index created.

SQL>  select object_name, last_ddl_time from user_objects where object_name = 'MYTABLE_IDX';

OBJECT_NAME                    LAST_DDL_TIME
------------------------------ -----------------------------
MYTABLE_IDX                    17-APR-2008 13:26:17

SQL> alter index mytable_idx rebuild;

Index altered.

SQL>  select object_name, last_ddl_time from user_objects where object_name = 'MYTABLE_IDX';

OBJECT_NAME                    LAST_DDL_TIME
------------------------------ -----------------------------
MYTABLE_IDX                    17-APR-2008 13:27:07